Petter Laake

• Løvgren, Pia Jorde; Laake, Petter; Reitan, Solveig Merete Klæbo & Narud, Kjersti (2022). Use of assessment instruments in forensic evaluations of criminal responsibility in Norway. BMC Psychiatry. ISSN 1471-244X. 22(1), p. 1–14. doi: 10.1186/s12888-022-03831-4.
• Brevik, Thea Beate; Trope, Ameli; Laake, Petter & Bjørkly, Stål (2021). Does women’s screening history have any impact on mammography screening attendance after tailored education? : A systematic review and meta-analysis . Medical Care. ISSN 0025-7079. 59(10), p. 893–900. doi: 10.1097/MLR.0000000000001576. Show summary

  Background: Many ethnic minority women have low attendance at breast cancer screening. Objectives: This brief report explores whether women’s screening histories impact mammography screening attendance after tailored education. Research Design: Systematic searches were conducted in 5 databases. Randomized controlled trials of educational interventions tailored to ethnic minority women that measured attendance at mammography screening were eligible for inclusion. Data extraction and risk of bias assessment were performed independently. Data were combined in a meta-analysis by using random effects models. Heterogeneity was estimated by using I2 statistics. Results: Six studies with 3521 women were eligible for inclusion. The D+L pooled risk ratio (RR) for mammography attendance for never screened participants was 1.54 (95% confidence interval, 1.24–1.91; P<0.001), with low heterogeneity (I2=27.1%, P=0.231). The D+L pooled risk ratio for attendance for ever screened participants was 1.26 (95% confidence interval, 1.11–1.43; P<0.001), with low heterogeneity (I2=35.5%, P=0.213). Conclusions: Tailored education increased attendance at mammography by 54% among never screened women and 26% among ever screened women. Although these findings must be interpreted with caution, the findings suggest that women’s screening history is an important and ignored variable that affects how effective tailored education is on mammography screening attendance.

• Linge, Anita; Jensen, Chris; Laake, Petter & Bjørkly, Stål (2021). Lifestyle and work-related factors associated with work ability and work participation for people with obesity: A prospective observational study after vocational rehabilitation. Diabetes, Metabolic Syndrome and Obesity. ISSN 1178-7007. 14, p. 2943–2954. doi: 10.2147/DMSO.S311462. Full text in Research Archive
• Linge, Anita; Jensen, Chris; Laake, Petter & Bjørkly, Stål (2021). Changes to body mass index, work self-efficacy, health-related quality of life, and work participation in people with obesity after vocational rehabilitation : a prospective observational study . BMC Public Health. ISSN 1471-2458. 21, p. 1–11. doi: 10.1186/s12889-021-10954-y. Full text in Research Archive Show summary

  Background People on or at risk of sick leave from work due to obesity or obesity-related problems participated in a new vocational rehabilitation (VR). The study aimed to examine the outcome changes in the participants’ health-related quality of life (HRQoL), body mass index (BMI), return to work self-efficacy (RTWSE), work ability scale (WAS) and degree of work participation (DWP) after their participation in the 12-month VR programme. The secondary aim was to examine associations between the outcome changes and HRQoL at 12-month follow-up, measured with the HRQoL 15D instrument (15D). Methods This prospective observational study included 95 participants. The one-year multidisciplinary VR programme with an integrated work and lifestyle intervention included 4 weeks of inpatient stay followed-up by 5 meetings. A paired sample t-test was used to examine changes in HRQoL, BMI, RTWSE, WAS, and DWP between baseline and the 12-month follow-up. Multiple linear regression analyses explored associations between changes in HRQoL and the outcome variables. Results The participants achieved statistically significant changes in HRQoL (2.57, 95% CI: 1.35 to 3.79), BMI (− 2.33, 95% CI: − 3.10 to − 1.56), RTWSE (15.89, 95% CI: 4.07 to 27.71), WAS (1.51, 95% CI: 0.83 to 2.20) and DWP (18.69, 95% CI: 8.35 to 29.02). At 12 months, a significant association was found between HRQoL and BMI (B = − 0.34, 95% CI: − 0.65 to − 0.04), RTWSE (B = 0.02, 95% CI: 0.004 to 0.04), WAS (B = 0.91, 95% CI: 0.55 to 1.28), DWP (B = − 0.02, 95% CI: − 0.04 to 0.001) and work absence (B = − 0.01, 95% CI: − 0.02 to − 0.002). The regression model explained 71.8% of the HRQoL variance. Conclusion The results indicated positive changes in HRQoL, BMI, RTWSE, WAS and DWP from baseline to the 12-month follow-up. Factors associated with HRQoL at the 12-month follow-up were decreased BMI, increased RTWSE, improved WAS and reduced work absence. Future studies examining VR programmes with lifestyle interventions for people with obesity are recommended.

• Bjørkly, Stål; Laake, Petter; Roaldset, John Olav & Douglas, Kevin Stewart (2021). The Safe pilot study : a prospective naturalistic study with repeated measures design to test the psychosis - violence link in and after discharge from forensic facilities. Psychiatry Research. ISSN 0165-1781. 298(April), p. 1–7. doi: 10.1016/j.psychres.2021.113793. Full text in Research Archive Show summary

  The research evidence is very strong for high recidivism rates of violence after discharge from forensic facilities. Big data research has found that a substantial proportion of the forensic population with relapse into violence has a psychosis diagnosis and a criminal record. However, more research on the association between psychotic symptoms and violence may inform and enhance risk assessment, prevention, and treatment. We conducted a prospective naturalistic study with a repeated measures design in a sample of 22 psychotic patients during follow-up after discharge from forensic mental health facilities. We had three aims: to test the predictive validity of three psychotic symptom scales for violence, to analyze main and interaction effects between psychotic symptoms and previous criminal conviction, and to explore the feasibility and potential benefit of the repeated measures design for prospective follow-up research. Interpreted within the limitation of the small sample size, the results were promising for all scales, particularly for adjusted effects without interaction. Two scales remained significant when their interaction with criminal conviction was adjusted. This indicates that risk judgment of psychotic patients with criminal conviction can be improved by adding measurement of fluctuations in psychotic symptoms. The repeated measures design was instrumental in this research. Keywords: forensic mental health, repeated measures, discharge, psychotic symptoms, criminality, violence

• Mundal, Ingunn Pernille; Laake, Petter; Mezzich, Juan; Bjørkly, Stål & Lara Cabrera, Mariela Loreto (2021). Assessment of the quality of life in parents of children with ADHD : validation of the Multicultural Quality of Life in Norwegian pediatric mental health settings. Frontiers in Psychology. ISSN 1664-1078. 12:638006, p. 1–10. doi: 10.3389/fpsyg.2021.638006. Full text in Research Archive
• Løvgren, Pia Jorde; Laake, Petter; Reitan, Solveig Merete Klæbo & Narud, Kjersti (2020). Assessing psychotic symptoms in forensic evaluations of criminal responsibility–a pilot study using Positive And Negative Syndrome Scale. Journal of Forensic Psychiatry & Psychology. ISSN 1478-9949. 31(4), p. 490–502. doi: 10.1080/14789949.2020.1771402. Full text in Research Archive
• Brevik, Thea Beate; Laake, Petter & Bjørkly, Stål (2020). Effect of culturally tailored education on attendance at mammography and the Papanicolaou test. Health Services Research (HSR). ISSN 0017-9124. 55(3), p. 457–468. doi: 10.1111/1475-6773.13271. Full text in Research Archive
• Lydersen, Stian; Fagerland, Morten & Laake, Petter (2019). Alternativer til Fishers eksakte test. Tidsskrift for Den norske legeforening. ISSN 0029-2001. 139(14), p. 1397–1397. doi: 10.4045/tidsskr.19.0238. Full text in Research Archive
• Wierenga, Lara M.; Sexton, Joseph; Laake, Petter; Giedd, Jay N. & Tamnes, Christian Krog (2018). A Key Characteristic of Sex Differences in the Developing Brain: Greater Variability in Brain Structure of Boys than Girls . Cerebral Cortex. ISSN 1047-3211. 28(8), p. 2741–2751. doi: 10.1093/cercor/bhx154. Full text in Research Archive
• Kristoffersen, Doris Tove; Helgeland, Jon; Clench-Aas, Jocelyne; Laake, Petter & Veierød, Marit Bragelien (2018). Observed to expected or logistic regression to identify hospitals with high or low 30-day mortality? PLOS ONE. ISSN 1932-6203. 13(4). doi: 10.1371/journal.pone.0195248. Full text in Research Archive Show summary

  Introduction A common quality indicator for monitoring and comparing hospitals is based on death within 30 days of admission. An important use is to determine whether a hospital has higher or lower mortality than other hospitals. Thus, the ability to identify such outliers correctly is essential. Two approaches for detection are: 1) calculating the ratio of observed to expected number of deaths (OE) per hospital and 2) including all hospitals in a logistic regression (LR) comparing each hospital to a form of average over all hospitals. The aim of this study was to compare OE and LR with respect to correctly identifying 30-day mortality outliers. Modifications of the methods, i.e., variance corrected approach of OE (OE-Faris), bias corrected LR (LR-Firth), and trimmed mean variants of LR and LR-Firth were also studied. Materials and methods To study the properties of OE and LR and their variants, we performed a simulation study by generating patient data from hospitals with known outlier status (low mortality, high mortality, non-outlier). Data from simulated scenarios with varying number of hospitals, hospital volume, and mortality outlier status, were analysed by the different methods and compared by level of significance (ability to falsely claim an outlier) and power (ability to reveal an outlier). Moreover, administrative data for patients with acute myocardial infarction (AMI), stroke, and hip fracture from Norwegian hospitals for 2012–2014 were analysed. Results None of the methods achieved the nominal (test) level of significance for both low and high mortality outliers. For low mortality outliers, the levels of significance were increased four- to fivefold for OE and OE-Faris. For high mortality outliers, OE and OE-Faris, LR 25% trimmed and LR-Firth 10% and 25% trimmed maintained approximately the nominal level. The methods agreed with respect to outlier status for 94.1% of the AMI hospitals, 98.0% of the stroke, and 97.8% of the hip fracture hospitals. Conclusion We recommend, on the balance, LR-Firth 10% or 25% trimmed for detection of both low and high mortality outliers

• Bærug, Anne Bergljot; Sletner, Line; Laake, Petter; Fretheim, Atle; Løland, Beate Fossum & Waage, Christin [Show all 8 contributors for this article] (2018). Recent gestational diabetes was associated with mothers stopping predominant breastfeeding earlier in a multi-ethnic population. Acta Paediatrica. ISSN 0803-5253. 107(6), p. 1028–1035. doi: 10.1111/apa.14274. Full text in Research Archive
• Bærug, Anne Bergljot; Laake, Petter; Løland, Beate Fossum; Tylleskär, Thorkild; Tufte, Elisabeth & Fretheim, Atle (2017). Explaining socioeconomic inequalities in exclusive breast feeding in Norway. Archives of Disease in Childhood. ISSN 0003-9888. 102(8), p. 708–714. doi: 10.1136/archdischild-2016-312038.
• Paur, Ingvild; Lilleby, Wolfgang; Bøhn, Siv Kjølsrud; Hulander, Erik; Klein, Willibrord & Vlatkovic, Ljiljana [Show all 19 contributors for this article] (2016). Tomato-based randomized controlled trial in prostate cancer patients: Effect on PSA. Clinical Nutrition. ISSN 0261-5614. 36(3), p. 672–679. doi: 10.1016/j.clnu.2016.06.014. Full text in Research Archive
• Fagerland, Morten; Lydersen, Stian & Laake, Petter (2015). Recommended confidence intervals for two independent binomial proportions. Statistical Methods in Medical Research. ISSN 0962-2802. 24(2), p. 224–254. doi: 10.1177/0962280211415469.
• Buonaccorsi, John P.; Dalen, Ingvild; Laake, Petter; Hjartåker, Anette; Engeset, Dagrun & Thoresen, Magne (2015). Sensitivity of regression calibration to non-perfect validation data with application to the Norwegian Women and Cancer Study. Statistics in Medicine. ISSN 0277-6715. 34(8), p. 1389–1403. doi: 10.1002/sim.6420.
• Lehre, Anne- Catherine W G; Hansen, Arvid Hedley; Lehre, Knut Petter Dæhlin & Laake, Petter (2014). Effects of the 2003 Quality Reform on Gender Gaps in Student Learning Outcomes in Norwegian Higher Education. Scandinavian Journal of Educational Research. ISSN 0031-3831. 58(3), p. 315–336. doi: 10.1080/00313831.2012.732602.
• Buonaccorsi, John P.; Laake, Petter & Veierød, Marit Bragelien (2014). On the power of the Cochran-Armitage test for trend in the presence of misclassification. Statistical Methods in Medical Research. ISSN 0962-2802. 3, p. 218–243. doi: 10.1177/0962280211406424.
• Lehre, Anne- Catherine W G; Laake, Petter & Sexton, Joseph Andrew (2014). Using Quantile Distance Functions to Assess Inter- and Intrasex Variability in PISA Achievement Scores. In Strietholt, Rolf; Bos, Wilfred; Gustafsson, Jan-Eric & Rosén, Monica (Ed.), Educational Policy Evaluation through International Comparative Assessments. Waxmann Verlag. ISSN 978-3-8309-3091-4. p. 177–190.
• Birkeflet, Oddveig; Laake, Petter & Vøllestad, Nina Køpke (2014). Poor multi-rater reliability in TCM pattern diagnoses and variation in the use of symptoms to obtain a diagnosis. Acupuncture in Medicine. ISSN 0964-5284. 32(4), p. 325–332. doi: 10.1136/acupmed-2013-010473.
• Buonaccorsi, John P.; Laake, Petter & Veierød, Marit Bragelien (2014). On the power of the Cochran-Armitage test for trend in the presence of misclassification. Statistical Methods in Medical Research. ISSN 0962-2802. 23(3), p. 218–243. doi: 10.1177/0962280211406424.
• Fagerland, Morten; Lydersen, Stian & Laake, Petter (2014). Recommended tests and confidence intervals for paired binomial proportions. Statistics in Medicine. ISSN 0277-6715. 33(16), p. 2850–2875. doi: 10.1002/sim.6148.
• Ringdal, Kjetil G.; Skaga, Nils Oddvar; Steen, Petter Andreas; Hestnes, Morten; Laake, Petter & Jones, J. Mary [Show all 7 contributors for this article] (2013). Classification of comorbidity in trauma: The reliability of pre-injury ASA physical status classification. Injury. ISSN 0020-1383. 44(1), p. 29–35. doi: 10.1016/j.injury.2011.12.024.
• Fagerland, Morten; Lydersen, Stian & Laake, Petter (2013). The McNemar test for binary matched-pairs data: mid-p and asymptotic are better than exact conditional. BMC Medical Research Methodology. ISSN 1471-2288. 13. doi: 10.1186/1471-2288-13-91. Full text in Research Archive
• Lehre, Anne- Catherine W G; Laake, Petter & Sexton, Joseph (2013). Differences in birth weight by sex using adjusted quantile distance functions. Statistics in Medicine. ISSN 0277-6715. 32(17), p. 2962–2970. doi: 10.1002/sim.5744.
• Karlsen, Anette; Svendsen, Mette; Seljeflot, Ingebjørg; Laake, Petter; Duttaroy, Asim K. & Drevon, Christian A [Show all 9 contributors for this article] (2013). Kiwifruit decreases blood pressure and whole-blood platelet aggregation in male smokers. Journal of Human Hypertension. ISSN 0950-9240. 27(2), p. 126–130. doi: 10.1038/jhh.2011.116.
• Fagerland, Morten; Eide, Geir Egil & Laake, Petter (2012). Linear regression. In Veierød, Marit Bragelien; Lydersen, Stian & Laake, Petter (Ed.), Medical statistics in clinical and epidemiological research. Gyldendal Akademisk. ISSN 9788205399594. p. 126–166.
• Lydersen, Stian; Fagerland, Morten & Laake, Petter (2012). Categorical data and contingency tables. In Veierød, Marit Bragelien; Lydersen, Stian & Laake, Petter (Ed.), Medical statistics in clinical and epidemiological research. Gyldendal Akademisk. ISSN 9788205399594. p. 48–89.
• Veierød, Marit Bragelien; Lydersen, Stian & Laake, Petter (2012). Design and analysis. In Veierød, Marit Bragelien; Lydersen, Stian & Laake, Petter (Ed.), Medical statistics in clinical and epidemiological research. Gyldendal Akademisk. ISSN 9788205399594. p. 23–44.
• Kristoffersen, Doris Tove; Helgeland, Jon; Clench-Aas, Jocelyne; Laake, Petter & Veierød, Marit Bragelien (2012). Comparing hospital mortality - how to count does matter for patients hospitalized for acute myocardial infarction (AMI), stroke and hip fracture. BMC Health Services Research. ISSN 1472-6963. 12. doi: 10.1186/1472-6963-12-364.
• Birkeflet, Oddveig; Laake, Petter & Vøllestad, Nina Køpke (2012). Traditional Chinese medicine patterns and recommended acupuncture points in infertile and fertile women. Acupuncture in Medicine. ISSN 0964-5284. 30(1), p. 12–16. doi: 10.1136/acupmed-2011-010089.
• Sexton, Joseph; Blomhoff, Rune; Karlsen, Anette & Laake, Petter (2012). Adaptive combination of dependent tests. Computational Statistics & Data Analysis. ISSN 0167-9473. 56(6), p. 1935–1943. doi: 10.1016/j.csda.2011.11.018.
• Sexton, Joseph & Laake, Petter (2012). Boosted coefficient models. Statistics and computing. ISSN 0960-3174. 22(4), p. 867–876. doi: 10.1007/s11222-011-9253-0.
• Haj Yasein, Nadia Nabil; Vindedal, Gry Fluge; Eilert-Olsen, Martine; Gundersen, Georg Andreas; Skare, Øivind & Laake, Petter [Show all 11 contributors for this article] (2011). Glial-conditional deletion of aquaporin-4 (Aqp4) reduces blood-brain water uptake and confers barrier function on perivascular astrocyte endfeet. Proceedings of the National Academy of Sciences of the United States of America. ISSN 0027-8424. 108(43), p. 17815–17820. doi: 10.1073/pnas.1110655108.
• Karlsen, Anette; Svendsen, Mette; Seljeflot, Ingebjørg; Sommernes, Mary-Ann; Sexton, Joseph & Brevik, Asgeir [Show all 23 contributors for this article] (2011). Compliance, tolerability and safety of two antioxidant-rich diets: a randomised controlled trial in male smokers. British Journal of Nutrition. ISSN 0007-1145. 106(4), p. 557–571. doi: 10.1017/S0007114511000353.
• Lehre, Anne- Catherine W G; Rowley, Nicole; Zhou, Yun; Holmseth, Silvia; Guo, Chungang & Holen, Torgeir [Show all 16 contributors for this article] (2011). Deletion of the betaine-GABA transporter (BGT1; slc6a12) gene does not affect seizure thresholds of adult mice. Epilepsy Research. ISSN 0920-1211. 95(1-2), p. 70–81. doi: 10.1016/j.eplepsyres.2011.02.014.
• Birkeflet, Oddveig; Laake, Petter & Vøllestad, Nina Køpke (2011). Low inter-rater reliability in traditional Chinese medicine for female infertility. Acupuncture in Medicine. ISSN 0964-5284. 29(1), p. 51–57. doi: 10.1136/aim.2010.003186.
• Frøslie, Kathrine Frey; Røislien, Jo; Laake, Petter; Henriksen, Tore; Qvigstad, Elisabeth & Veierød, Marit Bragelien (2010). Categorisation of continuous exposure variables revisited. A response to the Hyperglycaemia and Adverse Pregnancy Outcome (HAPO) Study. BMC Medical Research Methodology. ISSN 1471-2288. 10. doi: 10.1186/1471-2288-10-103.
• Bøhn, Siv Kjølsrud; Myhrstad, Mari Charlotte; Thoresen, Magne; Holden, Marit; Karlsen, Anette & Tunheim, Siv Haugen [Show all 17 contributors for this article] (2010). Blood cell gene expression associated with cellular stress defense is modulated by antioxidant-rich food in a randomised controlled clinical trial of male smokers. BMC Medicine. ISSN 1741-7015. 8. doi: 10.1186/1741-7015-8-54.
• Kjelsberg, Ellen & Laake, Petter (2010). Is the high mortality risk in sentenced offenders independent of previous imprisonment? European Journal of Epidemiology (EJE). ISSN 0393-2990. 25(4), p. 237–243. doi: 10.1007/s10654-010-9436-6.
• Karlsen, Anette; Paur, Ingvild; Bøhn, Siv Kjølsrud; Sakhi, Amrit Kaur; Borge, Grethe iren andersen & Serafini, Mauro [Show all 10 contributors for this article] (2010). Bilberry juice modulates plasma concentration of NF-kappa B related inflammatory markers in subjects at increased risk of CVD. European Journal of Nutrition. ISSN 1436-6207. 49(6), p. 345–355. doi: 10.1007/s00394-010-0092-0.
• Utvik, Jo Kristian; Haglerød, Camilla Margrete; Mylonakou, Maria-Niki; Holen, Torgeir; Kropf, Michel & Hirling, H [Show all 11 contributors for this article] (2009). Neuronal enriched endosomal protein of 21 kDa colocalizes with glutamate receptor subunit GLUR2/3 at the postsynaptic membrane. Neuroscience. ISSN 0306-4522. 158(1), p. 96–104. doi: 10.1016/j.neuroscience.2008.11.030.
• Haglerød, Camilla Margrete; Kapica, Aida; Boulland, Jean-Luc; Hussain, Suleman; Holen, Torgeir & Skare, Øivind [Show all 10 contributors for this article] (2009). Protein interacting with C kinase 1 (PICK1) and GluR2 are associated with presynaptic plasma membrane and vesicles in hippocampal excitatory synapses. Neuroscience. ISSN 0306-4522. 158(1), p. 242–252. doi: 10.1016/j.neuroscience.2008.11.029.
• Kaufmann, Walter A.; Ferraguti, Francesco; Fukazawa, Yugo; Kasugai, Yu; Shigemoto, Ryuichi & Laake, Petter [Show all 12 contributors for this article] (2009). Large-Conductance Calcium-Activated Potassium Channels in Purkinje Cell Plasma Membranes Are Clustered at Sites of Hypolemmal Microdomains. Journal of Comparative Neurology. ISSN 0021-9967. 515(2), p. 215–230. doi: 10.1002/cne.22066.
• Lydersen, Stian; Fagerland, MW & Laake, P (2009). Recommended tests for association in 2 x 2 tables. Statistics in Medicine. ISSN 0277-6715. 28(7), p. 1159–1175. doi: 10.1002/sim.3531.
• Lehre, Anne- Catherine W G; Lehre, Knut Petter Dæhlin; Laake, Petter & Danbolt, Niels Christian (2009). Greater Intrasex Phenotype Variability in Males Than in Females is a Fundamental Aspect of the Gender Differences in Humans. Developmental Psychobiology. ISSN 0012-1630. 51(2), p. 198–206. doi: 10.1002/dev.20358.
• Lehre, Anne- Catherine W G; Hansen, Arvid Hedley & Laake, Petter (2009). Gender and the 2003 Quality Reform in higher education in Norway. Higher Education. ISSN 0018-1560. 58(5), p. 585–597. doi: 10.1007/s10734-009-9211-3.
• Parr, CL; Hjartaker, A; Hjartåker, Anette; Laake, Petter; Lund, Eiliv & Veierod, MB [Show all 7 contributors for this article] (2009). Recall Bias in Melanoma Risk Factors and Measurement Error Effects: A Nested Case-Control Study Within the Norwegian Women and Cancer Study. American Journal of Epidemiology. ISSN 0002-9262. 169(3), p. 257–266. doi: 10.1093/aje/kwn363.
• Sexton, Joseph & Laake, Petter (2009). Stochastic Approximation Boosting for Incomplete Data Problems. Biometrics. ISSN 0006-341X. 65(4), p. 1156–1163. doi: 10.1111/j.1541-0420.2009.01202.x.
• Sexton, Joseph & Laake, Petter (2009). Standard errors for bagged and random forest estimators. Computational Statistics & Data Analysis. ISSN 0167-9473. 53(3), p. 801–811. doi: 10.1016/j.csda.2008.08.007.
• Dalen, Ingvild; Buonaccorsi, JP; Sexton, Joseph; Laake, Petter & Thoresen, Magne (2009). Correction for misclassification of a categorized exposure in binary regression using replication data. Statistics in Medicine. ISSN 0277-6715. 28(27), p. 3386–3410. doi: 10.1002/sim.3712.
• Karlsen, Anette; Svendsen, Mette; Brevik, Asgeir; Bøhn, Siv K; Myhrstad, Mari C.W. & Thoresen, Magne [Show all 19 contributors for this article] (2008). Dietary intake of antioxidant-rich foods increase plasma antioxidants, enhance DNA repair capacity and reduce blood pressure in smoking, middle-aged men, PhD Thesis. Universitetet i Oslo, Institutt for ernæringsforskning.
• Benestad, Haakon Breien & Laake, Petter (2008). Forskning: metode og planlegging. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Forskning i medisin og biofag. 2. utgave. Gyldendal Akademisk. ISSN 978-82-05-38487-3.
• Thelle, Dag Steinar & Laake, Petter (2008). Epidemiologisk forskning: begreper og metoder. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Forskning i medisin og biofag. 2. utgave. Gyldendal Akademisk. ISSN 978-82-05-38487-3.
• Laake, Petter & Skovlund, Eva (2008). Statistisk analyse av kontinuerlige data. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Forskning i medisin og biofag. 2. utgave. Gyldendal Akademisk. ISSN 978-82-05-38487-3.
• Laake, Petter & Egeland, Thore (2008). Statistisk analyse av kategoriske data. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Forskning i medisin og biofag. 2. utgave. Gyldendal Akademisk. ISSN 978-82-05-38487-3.
• Utne, Peder Heyerdahl; Thelle, Dag Steinar & Laake, Petter (2008). Kvalitetssikring av forskning. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Forskning i medisin og biofag. 2. utgave. Gyldendal Akademisk. ISSN 978-82-05-38487-3.
• Olsen, Bjørn Reino; Laake, Petter & Ottersen, Ole Petter (2008). Søknad om forskningsmidler. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Forskning i medisin og biofag. 2. utgave. Gyldendal Akademisk. ISSN 978-82-05-38487-3.
• Sexton, Joseph & Laake, Petter (2008). LogitBoost with errors-in-variables. Computational Statistics & Data Analysis. ISSN 0167-9473. 52. doi: 10.1016/j.csda.2007.09.004.
• Parr, CL; Hjartåker, Anette; Hjartaker, A; Scheel, Ida; Lund, Eiliv & Laake, Petter [Show all 8 contributors for this article] (2008). Comparing methods for handling missing values in food-frequency questionnaires and proposing k nearest neighbours imputation: effects on dietary intake in the Norwegian Women and Cancer study (NOWAC). Public Health Nutrition. ISSN 1368-9800. 11, p. 361–370. doi: 10.1017/S1368980007000365.
• Laake, Petter; Hjartåker, Anette; Thelle, Dag Steinar & Veierød, Marit Bragelien (2007). Epidemiologisk og klinisk forskning. In Laake, Petter; Hjartåker, Anette; Thelle, Dag Steinar & Veierød, Marit Bragelien (Ed.), Epidemiologiske og kliniske forskningsmetoder. Gyldendal Akademisk. ISSN 978-82-05-33505-9. p. 33–44.
• Laake, Petter; Thoresen, Magne & Veierød, Marit Bragelien (2007). Målefeilsproblemer. In Laake, Petter; Hjartåker, Anette; Thelle, Dag Steinar & Veierød, Marit Bragelien (Ed.), Epidemiologiske og kliniske forskningsmetoder. Gyldendal Akademisk. ISSN 978-82-05-33505-9. p. 128–168.
• Veierød, Marit Bragelien & Laake, Petter (2007). Regresjonsmodeller og analyse av sammenheng mellom eksponering og sykdom. In Laake, Petter; Hjartåker, Anette; Thelle, Dag Steinar & Veierød, Marit Bragelien (Ed.), Epidemiologiske og kliniske forskningsmetoder. Gyldendal Akademisk. ISSN 978-82-05-33505-9. p. 66–127.
• Svensson, Elisabeth; Hjartåker, Anette & Laake, Petter (2007). Hva skal måles og hvordan? In Laake, Petter; Hjartåker, Anette; Thelle, Dag Steinar & Veierød, Marit Bragelien (Ed.), Epidemiologiske og kliniske forskningsmetoder. Gyldendal Akademisk. ISSN 978-82-05-33505-9. p. 45–65.
• Laake, Petter; Egeland, Thore & Skovlund, Eva (2007). Statistical issues. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Research Methodology in the Medical and Biological Sciences. Academic Press. ISSN 978-0-12-373874-5. p. 311–364.
• Benestad, Haakon Breien & Laake, Petter (2007). Reseach methodology: Strategies, planning and analysis. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Research Methodology in the Medical and Biological Sciences. Academic Press. ISSN 978-0-12-373874-5. p. 93–124.
• Thelle, Dag Steinar & Laake, Petter (2007). Epidemiology: Concepts and methods. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Research Methodology in the Medical and Biological Sciences. Academic Press. ISSN 978-0-12-373874-5. p. 241–280.
• Olsen, Bjørn Reino; Laake, Petter & Ottersen, Ole Petter (2007). Guide to grant applications. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Research Methodology in the Medical and Biological Sciences. Academic Press. ISSN 978-0-12-373874-5. p. 433–456.
• Lydersen, Stian; Pradhan, Vivek; Enchaudhuri, PS; Senchaudhuri, Pralay & Laake, Petter (2007). Choice of test for association in small sample unordered r × c tables. Statistics in Medicine. ISSN 0277-6715. 26(23), p. 4328–4343. doi: 10.1002/sim.2839.

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• Fagerland, Morten; Lydersen, Stian & Laake, Petter (2017). Statistical Analysis of Contingency Tables. CRC Press. ISBN 978-1-4665-8817-2. 634 p.
• Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (2015). Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication. Academic Press. ISBN 978-0-12-799943-2. 566 p.
• Veierød, Marit Bragelien; Lydersen, Stian & Laake, Petter (2012). Medical statistics in clinical and epidemiological research. Gyldendal Akademisk. ISBN 9788205399594. 720 p.
• Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (2008). Forskning i medisin og biofag. 2. utgave. Gyldendal Akademisk. ISBN 978-82-05-38487-3. 550 p.
• Laake, Petter & Valen, Guro (2008). Fra basalmedisinsk til klinisk forskning. Gyldendal Akademisk. ISBN 978-82-05-38487-3. 14 p. Show summary

  Boka Forskning i medisin og biofag er grunnbok til Det medisinske fakultets forskerutdannelse, obligatorisk kurs. Innskrevet et nytt kapitel om translasjonsforskning

• Laake, Petter; Hjartåker, Anette; Thelle, Dag S. & Veierød, Marit B. (2007). Epidemiologiske og kliniske forskningsmetoder. Gyldendal Akademisk. ISBN 9788205335059. 551 p.

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• Leoncio Netto, Waldir; Fagerland, Morten; Lydersen, Stian; Laake, Petter & Lingjærde, Ole Christian (2022). contingencytables: Statistical Analysis of Contingency Tables.
• Sandvig, Heidi Vihovde & Laake, Petter (2019). Ikke faglig begrunnet styrevedtak om fødesammenslåing. Dagens medisin. ISSN 1501-4290.
• Lydersen, Stian; Fagerland, Morten & Laake, Petter (2019). Pearsons khikvadrattest. Tidsskrift for Den norske legeforening. ISSN 0029-2001. 139(12), p. 1183–1183. doi: 10.4045/tidsskr.18.0125.
• Lydersen, Stian; Fagerland, Morten & Laake, Petter (2019). Fishers eksakte test - hvordan smaker teen? Tidsskrift for Den norske legeforening. ISSN 0029-2001. 139(13), p. 1292–1292. doi: 10.4045/tidsskr.19.0237.
• Lydersen, Stian; Fagerland, Morten & Laake, Petter (2018). Evaluation of methods for analysis of 2x2 contingency tables. Show summary

  Evaluation of methods for analysis of 2x2 contingency tables Introduction: Literally hundreds of methods for hypothesis tests and confidence intervals for contingency tables are described in the literature. This is the case even for the seemingly simple 2 × 2 table. The Pearson chi squared test, the Fisher exact test, and the Wald confidence interval are widely used methods. Unfortunately, these methods are also commonly used in situations when they perform poorly, and better alternatives exist. Aims: To show how to evaluate and choose appropriate methods for hypothesis testing and confidence interval estimation for 2x2 tables Methods: Important properties of a hypothesis test are the actual significance level and power. Important properties for a confidence interval are coverage probability, expected interval width, and symmetry. We have studied these properties for alternative methods. Conclusion: For large samples, the asymptotic Pearson chi squared test performs well. Yates’s continuity correction should never be used. In small samples, the traditional advice is the Fisher exact test. But unconditional tests are generally more powerful than Fisher’s exact test for small samples. Unconditional tests also preserve the significance level. That is, the actual significance level does not exceed the nominal significance level, which is often 5%. Unconditional tests were but previously disadvantaged by being computationally demanding. Alternatively, Fisher’s exact test with mid-p adjustment is easy to compute, and gives approximately the same results as an unconditional test. The Wald confidence interval is a traditional choice for the difference between two proportions. But its coverage can dip substantially below the nominal coverage, which is usually 95%. The Agresti-Caffo interval and the Newcombe hybrid score interval are also easy to compute with closed form expressions. They have better coverage, and also narrower expected interval width, and better symmetry than the Wald interval. Reference: Fagerland MW, Lydersen S, Laake P (2017). Statistical Analysis of Contingency Tables. Chapman and Hall/CRC.

• Kristoffersen, Doris Tove; Helgeland, Jon; Clench-Aas, Jocelyne; Laake, Petter & Veierød, Marit Bragelien (2016). Type I error and power for detecting hospitals with high or low 30-day mortality.
• Fagerland, Morten Wang; Lydersen, Stian & Laake, Petter (2015). Confidence Intervals for Two Independent Binomial Proportions. In Balakrishnan, N.; Brandimarte, Paolo; Everitt, Brian S.; Molenberghs, Geert; Piegorsch, Walter W. & Ruggeri, Fabrizio (Ed.), Wiley StatsRef: Statistics Reference Online. John Wiley & Sons. ISSN 9781118445112. doi: 10.1002/9781118445112.stat08007.
• Laake, Petter & Fagerland, Morten (2015). Statistical Inference. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication.. Academic Press. ISSN 978-0-12-799943-2. p. 379–430.
• Holm, Søren; Hofmann, Bjørn & Laake, Petter (2015). Ethics and Scientific Conduct. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication.. Academic Press. ISSN 978-0-12-799943-2. p. 43–70.
• Thelle, Dag Steinar & Laake, Petter (2015). Epidemiology. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication.. Academic Press. ISSN 978-0-12-799943-2. p. 275–320.
• Benestad, Haakon Breien & Laake, Petter (2015). Research Strategies, Planning and Analysis. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication.. Academic Press. ISSN 978-0-12-799943-2. p. 89–104.
• Olsen, Bjørn Reino; Laake, Petter & Ottersen, Ole Petter (2015). Guide to Grant Applications. In Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (Ed.), Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication.. Academic Press. ISSN 978-0-12-799943-2. p. 519–546.
• Benestad, Haakon Breien & Laake, Petter (2014). Dårlig tittel - dårlig manus? Tidsskrift for Den norske legeforening. ISSN 0029-2001. 134(4), p. 382–382. doi: 10.4045/tidsskr.14.0143.
• Lehre, Anne- Catherine W G; Hansen, Arvid Hedley; Lehre, Knut Petter Dæhlin & Laake, Petter (2012). Gender gap in Norwegian Higher Education.
• Thelle, Dag S. & Laake, Petter (2011). Fra ammetåke til klarsyn. Forskning.no. ISSN 1891-635X.
• Lydersen, Stian; Laake, Petter & Fagerland, Morten (2011). The analysis of 2 x 2 contingency tables-yet again: Author's reply. Statistics in Medicine. ISSN 0277-6715. 30(8), p. 891–892. doi: 10.1002/sim.4135.
• Lehre, Anne- Catherine W G; Lehre, Knut Petter Dæhlin; Hansen, Arvid Hedley; Laake, Petter & Danbolt, Niels Christian (2010). Gender: Males are more extreme.
• Karlsen, Anette; Lilleby, Wolfgang; Klein, Willibrord; Laake, Petter; Fosså, Sophie Dorothea & Eri, Lars Magne [Show all 9 contributors for this article] (2010). A phase I/II randomized controlled trial investigating the effects of two dietary intervention strategies in prostate cancer patients.
• Laake, Petter & Thelle, Dag Steinar (2010). Are mid-pregnancy androgen levels negatively associated with breastfeeding? Acta Obstetricia et Gynecologica Scandinavica. ISSN 0001-6349. 89(5), p. 722–723. doi: 10.3109/00016341003657942.
• Parr, Christine Louise; Hjartåker, Anette; Laake, Petter; Lund, Eiliv & Veierød, Marit Bragelien (2009). Recall bias in melanoma risk factors and measurement error effects: a nested case-control study within the Norwegian Women and Cancer Study. Norsk Epidemiologi, Supplement. ISSN 0803-4206. 19, p. 8–8.
• Parr, CL; Hjartaker, A; Hjartåker, Anette; Laake, Petter; Lund, Eiliv & Veierod, MB [Show all 7 contributors for this article] (2009). Parr et al. Respond to "Recall Bias in Melanoma". American Journal of Epidemiology. ISSN 0002-9262. 169(3), p. 271–272. doi: 10.1093/aje/kwn356.
• Karlsen, Anette; Paur, Ingvild; Bøhn, Siv Kjølsrud; Sakhi, Amrit Kaur; Grethe Iren, Borge & Serafini, Mauro [Show all 10 contributors for this article] (2009). Bilberry juice modulate plasma concentration of NF- related inflammatory markers in subjects at increased risk of CVD.
• Bøhn, Siv Kjølsrud; Myhrstad, Mari Charlotte; Thoresen, Magne; Holden, Marit; Tunheim, Siv Haugen & Karlsen, Anette [Show all 16 contributors for this article] (2008). Plant food phytochemicals modulate gene expression in human blood cells.
• Lehre, Anne- Catherine W G; Laake, Petter & Danbolt, Niels Christian (2011). Sex matters: Looking into variability. The variability hypothesis, the 2003 Quality Reform in higher education in Norway, and the role of BGT1 in seizure control. Unipub forlag. ISSN 978-82-8264-149-4.
• Roaldset, John Olav; Gøtestam, K Gunnar; Holen, Are; Bjørkly, Stål & Laake, Petter (2010). Risk assessment of violent, suicidal and self-injurious behaviour in acute psychiatry - a bio-psycho-social approach. Norwegian University of Science and Technology. ISSN 978-82-471-2492-5. Show summary

  Recently, psychiatric hospitals in Norway have been criticised for premature discharges and for poor assessments of patients’ risks of violence or self-harm. Due to the high turnover of patients and the obligation to admit all acutely ill patients who are in need of hospitalisation, the acute wards are particularly exposed to such criticism. Unstructured clinical judgements alone still appear to be the dominant approach to risk assessments. Currently used instruments for risk assessment are time consuming, and their use require special expertise. The goal of the “Risk Project” at Ålesund Hospital was early identification of patients in need of risk assessments. Various screening methods were tested in a prospective, naturalistic design. This dissertation is a part of the larger Risk Project. In the dissertation, different approaches towards risk analyses of violence, suicide and self-injury were examined: (i) Biologically based, in which lipids and serotonin are measured in the blood; (ii) Patient based, in which patients’ self-reports of risk (SRS) are employed, and (iii) Structured professional, by applying a violence screening instrument developed for use in acute psychiatry (V-RISK-10). SRS and V-RISK-10 were scored both at the time of admittance and discharge. Blood was drawn at admission. These measures were then compared with the episodes of violent, suicidal and self-injurious behaviour recorded during the patient’s hospital stay and also, during the first year after discharge. The study sample for the biological markers and the SRSs included all of the acutely admitted patients during one year (n=489) in one acute psychiatric unit. The V-RISK-10 study included all admissions of two units (n=1017). The numbers of patients who completed the study were 254 during their hospital stay and 196 after discharge, all with regard to lipids/serotonin, 429 and 266 for SRS, and 980 and 381 for V-RISK-10, respectively. Similar to findings from other studies, low concentrations of total cholesterol were found to predict inpatient suicidal and violent behaviour and also, violent behaviour three months after discharge. Low HDL levels were predictive of violence repeaters. High triglyceride levels predicted self-injurious behaviour (SIB) during the hospital stay, and both suicidal behaviour and SIB during the first year after discharge. The best results were obtained among patients who had recorded episodes of both suicidal behaviour and SIB. This finding contradicts prior studies on self-harm but concurs with three recent studies that look at the effects of short-term and chronic psychological stress. No significant correlations between serotonin levels and violence, suicidal behaviour or SIB were found in our sample. SRS predicted violence, suicidal behaviour and SIB both during the hospital stay and at three months after discharge. In addition, SRS of violence was also significant at 12 months after discharge. The accuracy was higher for self-harm during the hospital stays and for violence after discharge. We found no other validation studies of patients’ self-reported risk of suicide or violence. The predictive validity of the V-RISK-10 was equal to or better than those of the comprehensive risk assessment instruments, and it was very high in relation to severe violence. The screening instrument was sensitive to the risk of violence independent of gender and even for patients without any known history of violence. Despite significant findings for the lipids and SRS, these methods are not recommended for regular clinical use as single predictor variables, but they may be used together in combination with established risk procedures or clinical judgements. V-RISK-10 demonstrated good psychometric properties as a violence screening tool for acute psychiatry. Further research should be undertaken to confirm the findings.

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