Petter Laake

• 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), s 457- 468 . doi: 10.1111/1475-6773.13271
• Lydersen, Stian; Fagerland, Morten & Laake, Petter (2019). Alternativer til Fishers eksakte test. Tidsskrift for Den norske legeforening.  ISSN 0029-2001.  139(14), s 1397- 1397 . doi: 10.4045/tidsskr.19.0238
• Bærug, Anne Bergljot; Sletner, Line; Laake, Petter; Fretheim, Atle; Løland, Beate Fossum; Waage, Christin; Birkeland, Kåre I. & Jenum, Anne Karen (2018). Recent gestational diabetes was associated with mothers stopping predominant breastfeeding earlier in a multi-ethnic population. Acta Paediatrica.  ISSN 0803-5253.  107(6), s 1028- 1035 . doi: 10.1111/apa.14274 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

• 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), s 2741- 2751 . doi: 10.1093/cercor/bhx154 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), s 708- 714 . doi: 10.1136/archdischild-2016-312038
• Paur, Ingvild; Lilleby, Wolfgang; Bøhn, Siv Kjølsrud; Hulander, Erik; Klein, Willibrord; Vlatkovic, Ljiljana; Axcrona, Karol; Bolstad, Nils; Bjøro, Trine; Laake, Petter; Tasken, Kristin Austlid; Svindland, Aud; Eri, Lars Magne; Brennhovd, Bjørn; Carlsen, Monica Hauger; Fosså, Sophie Dorothea; Smeland, Sigbjørn; Karlsen, Anette Solli & Blomhoff, Rune (2016). Tomato-based randomized controlled trial in prostate cancer patients: Effect on PSA. Clinical Nutrition.  ISSN 0261-5614.  36(3), s 672- 679 . doi: 10.1016/j.clnu.2016.06.014 Full text in Research Archive.
• 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), s 1389- 1403 . doi: 10.1002/sim.6420
• 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), s 224- 254 . doi: 10.1177/0962280211415469
• 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), s 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), s 218- 243 . doi: 10.1177/0962280211406424
• 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, s 218- 243
• Fagerland, Morten; Lydersen, Stian & Laake, Petter (2014). Recommended tests and confidence intervals for paired binomial proportions. Statistics in Medicine.  ISSN 0277-6715.  33(16), s 2850- 2875 . doi: 10.1002/sim.6148
• 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), s 315- 336 . doi: 10.1080/00313831.2012.732602
• 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 Rolf Strietholt; Wilfred Bos; Jan-Eric Gustafsson & Monica Rosén (ed.),  Educational Policy Evaluation through International Comparative Assessments.  Waxmann Verlag.  ISBN 978-3-8309-3091-4.  Part B: Empirical Studies.  s 177 - 190
• 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.
• Karlsen, Anette; Svendsen, Mette; Seljeflot, Ingebjørg; Laake, Petter; Duttaroy, Asim K.; Drevon, Christian A; Arnesen, Harald; Tonstad, Serena & Blomhoff, Rune (2013). Kiwifruit decreases blood pressure and whole-blood platelet aggregation in male smokers. Journal of Human Hypertension.  ISSN 0950-9240.  27(2), s 126- 130 . doi: 10.1038/jhh.2011.116
• 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), s 2962- 2970 . doi: 10.1002/sim.5744
• Ringdal, Kjetil G.; Skaga, Nils Oddvar; Steen, Petter Andreas; Hestnes, Morten; Laake, Petter; Jones, J. Mary & Lossius, Hans Morten (2013). Classification of comorbidity in trauma: The reliability of pre-injury ASA physical status classification. Injury.  ISSN 0020-1383.  44(1), s 29- 35 . doi: 10.1016/j.injury.2011.12.024
• 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), s 12- 16 . doi: 10.1136/acupmed-2011-010089
• Fagerland, Morten; Eide, Geir Egil & Laake, Petter (2012). Linear regression, In Marit Bragelien Veierød; Stian Lydersen & Petter Laake (ed.),  Medical statistics in clinical and epidemiological research.  Gyldendal Akademisk.  ISBN 9788205399594.  Kapittel 4.  s 126 - 166
• 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
• Lydersen, Stian; Fagerland, Morten & Laake, Petter (2012). Categorical data and contingency tables, In Marit Bragelien Veierød; Stian Lydersen & Petter Laake (ed.),  Medical statistics in clinical and epidemiological research.  Gyldendal Akademisk.  ISBN 9788205399594.  Kapittel 2.  s 48 - 89
• Sexton, Joseph; Blomhoff, Rune; Karlsen, Anette & Laake, Petter (2012). Adaptive combination of dependent tests. Computational Statistics & Data Analysis.  ISSN 0167-9473.  56(6), s 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), s 867- 876 . doi: 10.1007/s11222-011-9253-0
• Veierød, Marit Bragelien; Lydersen, Stian & Laake, Petter (2012). Design and analysis, In Marit Bragelien Veierød; Stian Lydersen & Petter Laake (ed.),  Medical statistics in clinical and epidemiological research.  Gyldendal Akademisk.  ISBN 9788205399594.  kapittel 1.  s 23 - 44
• 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), s 51- 57 . doi: 10.1136/aim.2010.003186
• Haj Yasein, Nadia Nabil; Vindedal, Gry Fluge; Eilert-Olsen, Martine; Gundersen, Georg Andreas; Skare, Øivind; Laake, Petter; Klungland, Arne; Thoren, Anna; Burkhardt, John Michael; Ottersen, Ole Petter & Nagelhus, Erlend Arnulf (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), s 17815- 17820 . doi: 10.1073/pnas.1110655108
• Karlsen, Anette; Svendsen, Mette; Seljeflot, Ingebjørg; Sommernes, Mary-Ann; Sexton, Joseph; Brevik, Asgeir; Erlund, Iris; Serafini, Mauro; Bastani, Nasser Ezzatkhah; Remberg, Siv Fagertun; Borge, Grethe Iren Andersen; Carlsen, Monica Hauger; Bøhn, Siv Kjølsrud; Myhrstad, Mari; Dragsted, Lars; Duttaroy, Asim K.; Haffner, Karin; Laake, Petter; Drevon, Christian A; Arnesen, Harald; Collins, Andrew Richard; Tonstad, Serena & Blomhoff, Rune (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), s 557- 571 . doi: 10.1017/S0007114511000353
• Lehre, Anne- Catherine W G; Rowley, Nicole; Zhou, Yun; Holmseth, Silvia; Guo, Chungang; Holen, Torgeir; Hua, Rui; Laake, Petter; Olofsson, Anna Maria; Poblete-Naredo, Irais; Rusakov, Dimitri A.; Madsen, Karsten K.; Clausen, Rasmus P.; Schousboe, Arne; White, H. Steve & Danbolt, Niels Christian (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), s 70- 81 . doi: 10.1016/j.eplepsyres.2011.02.014
• Bøhn, Siv Kjølsrud; Myhrstad, Mari Charlotte; Thoresen, Magne; Holden, Marit; Karlsen, Anette; Tunheim, Siv Haugen; Erlund, Iris; Svendsen, Mette; Seljeflot, Ingebjørg; Moskaug, Jan Øivind; Duttaroy, Asim K.; Laake, Petter; Arnesen, Harald; Tonstad, Serena; Collins, Andrew Richard; Drevon, Christian A & Blomhoff, Rune (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
• 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
• Karlsen, Anette; Paur, Ingvild; Bøhn, Siv Kjølsrud; Sakhi, Amrit Kaur; Borge, Grethe iren andersen; Serafini, Mauro; Erlund, Iris; Laake, Petter; Tonstad, Serena & Blomhoff, Rune (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), s 345- 355 . doi: 10.1007/s00394-010-0092-0
• 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), s 237- 243 . doi: 10.1007/s10654-010-9436-6
• 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), s 3386- 3410 . doi: 10.1002/sim.3712
• Haglerød, Camilla Margrete; Kapica, Aida; Boulland, Jean-Luc; Hussain, Suleman; Holen, Torgeir; Skare, Øivind; Laake, Petter; Ottersen, Ole Petter; Haug, Finn-Mogens Smejda & Davanger, Svend (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), s 242- 252 . doi: 10.1016/j.neuroscience.2008.11.029
• Kaufmann, Walter A.; Ferraguti, Francesco; Fukazawa, Yugo; Kasugai, Yu; Shigemoto, Ryuichi; Laake, Petter; Sexton, Joseph A.; Ruth, Peter; Wietzorrek, Georg; Knaus, Hans Gunther; Storm, Johan Frederik & Ottersen, Ole Petter (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), s 215- 230 . doi: 10.1002/cne.22066
• 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), s 585- 597 . doi: 10.1007/s10734-009-9211-3
• 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), s 198- 206 . doi: 10.1002/dev.20358
• Lydersen, Stian; Fagerland, MW & Laake, P (2009). Recommended tests for association in 2 x 2 tables. Statistics in Medicine.  ISSN 0277-6715.  28(7), s 1159- 1175 . doi: 10.1002/sim.3531
• Parr, CL; Hjartåker, Anette; Hjartaker, A; Laake, Petter; Lund, Eiliv; Veierod, MB & 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. American Journal of Epidemiology.  ISSN 0002-9262.  169(3), s 257- 266 . doi: 10.1093/aje/kwn363
• Sexton, Joseph & Laake, Petter (2009). Standard errors for bagged and random forest estimators. Computational Statistics & Data Analysis.  ISSN 0167-9473.  53(3), s 801- 811 . doi: 10.1016/j.csda.2008.08.007
• Sexton, Joseph & Laake, Petter (2009). Stochastic Approximation Boosting for Incomplete Data Problems. Biometrics.  ISSN 0006-341X.  65(4), s 1156- 1163 . doi: 10.1111/j.1541-0420.2009.01202.x
• Utvik, Jo Kristian; Haglerød, Camilla Margrete; Mylonakou, Maria-Niki; Holen, Torgeir; Kropf, Michel; Hirling, H; Skare, Øivind; Laake, Petter; Ottersen, Ole Petter; Haug, Finn-Mogens Smejda & Davanger, Svend (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), s 96- 104 . doi: 10.1016/j.neuroscience.2008.11.030
• Benestad, Haakon Breien & Laake, Petter (2008). Forskning: metode og planlegging, I: Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (red.),  Forskning i medisin og biofag. 2. utgave.  Gyldendal Akademisk.  ISBN 978-82-05-38487-3.  Kapittel 4.
• Karlsen, Anette; Svendsen, Mette; Brevik, Asgeir; Bøhn, Siv K; Myhrstad, Mari C.W.; Thoresen, Magne; Seljeflot, Ingebjørg; Arnesen, Harald; Erlund, Iris; Serafini, Mauro; Remberg, Siv Fagertun; Haffner, Karin; Borge, Grethe Iren Andersen; Dragsted, Lars; Laake, Petter; Drevon, Christian A.; Collins, Andrew; Tonstad, Serena & Blomhoff, Rune (2008). Dietary intake of antioxidant-rich foods increase plasma antioxidants, enhance DNA repair capacity and reduce blood pressure in smoking, middle-aged men, In  PhD Thesis.  Universitetet i Oslo, Institutt for ernæringsforskning.  faglig_bok_institusjon.
• Laake, Petter & Egeland, Thore (2008). Statistisk analyse av kategoriske data, I: Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (red.),  Forskning i medisin og biofag. 2. utgave.  Gyldendal Akademisk.  ISBN 978-82-05-38487-3.  Kapittel 13.
• Laake, Petter & Skovlund, Eva (2008). Statistisk analyse av kontinuerlige data, I: Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (red.),  Forskning i medisin og biofag. 2. utgave.  Gyldendal Akademisk.  ISBN 978-82-05-38487-3.  Kapittel 12.
• Olsen, Bjørn Reino; Laake, Petter & Ottersen, Ole Petter (2008). Søknad om forskningsmidler, I: Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (red.),  Forskning i medisin og biofag. 2. utgave.  Gyldendal Akademisk.  ISBN 978-82-05-38487-3.  Kapittel 18.
• Parr, CL; Hjartaker, A; Hjartåker, Anette; Scheel, Ida; Lund, Eiliv; Laake, Petter; Veierød, Marit Bragelien & Veierod, MB (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, s 361- 370 . doi: 10.1017/S1368980007000365
• 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
• Thelle, Dag Steinar & Laake, Petter (2008). Epidemiologisk forskning: begreper og metoder, I: Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (red.),  Forskning i medisin og biofag. 2. utgave.  Gyldendal Akademisk.  ISBN 978-82-05-38487-3.  Kapittel 10.
• Utne, Peder Heyerdahl; Thelle, Dag Steinar & Laake, Petter (2008). Kvalitetssikring av forskning, I: Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (red.),  Forskning i medisin og biofag. 2. utgave.  Gyldendal Akademisk.  ISBN 978-82-05-38487-3.  Kapittel 17.
• Benestad, Haakon Breien & Laake, Petter (2007). Reseach methodology: Strategies, planning and analysis, In Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (ed.),  Research Methodology in the Medical and Biological Sciences.  Academic Press.  ISBN 978-0-12-373874-5.  4.  s 93 - 124
• Eid, T.; Hammer, Janniche; Runden, Elise; Roberg, B; Thomas, M. J.; Osen, K.; Davanger, S; Laake, Petter; Torgner, I. A.; Lee, Shih W; Lee, TS; Kim, Jung H; Spencer, D. D.; Ottersen, Ole Petter & de Lanerolle, Nihal C (2007). Increased expression of phosphate-activated glutaminase in hippocampal neurons in human mesial temporal lobe epilepsy. Acta Neuropathologica.  ISSN 0001-6322.  113(2), s 137- 152 . doi: 10.1007/s00401-006-0158-5
• Karlsen, Anette; Retterstol, L; Laake, Petter; Knudsen, Ingvild Paur; Bøhn, Siv Kjølsrud; Sandvik, L & Blomhoff, Rune (2007). Anthocyanins inhibit nuclear factor-kappa B activation in monocytes and reduce plasma concentrations of pro-inflammatory mediators in healthy adults. Journal of Nutrition.  ISSN 0022-3166.  137, s 1951- 1954
• Karlsen, Anette; Retterstøl, Lars; Laake, Petter; Bøhn, Siv Kjølsrud; Sandvik, Leiv & Blomhoff, Rune (2007). Effects of a daily intake of one glass of red wine on biomarkers of antioxidant status, oxidative stress and inflammation in healthy adults. e - SPEN: the European e-journal of clinical nutrition and metabolism.  ISSN 1751-4991.  2, s e127- e133
• Laake, Petter; Egeland, Thore & Skovlund, Eva (2007). Statistical issues, In Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (ed.),  Research Methodology in the Medical and Biological Sciences.  Academic Press.  ISBN 978-0-12-373874-5.  11.  s 311 - 364
• Laake, Petter; Hjartåker, Anette; Thelle, Dag Steinar & Veierød, Marit Bragelien (2007). Epidemiologisk og klinisk forskning, I: Petter Laake; Anette Hjartåker; Dag Steinar Thelle & Marit Bragelien Veierød (red.),  Epidemiologiske og kliniske forskningsmetoder.  Gyldendal Akademisk.  ISBN 978-82-05-33505-9.  1.  s 33 - 44
• Laake, Petter; Thoresen, Magne & Veierød, Marit Bragelien (2007). Målefeilsproblemer, I: Petter Laake; Anette Hjartåker; Dag Steinar Thelle & Marit Bragelien Veierød (red.),  Epidemiologiske og kliniske forskningsmetoder.  Gyldendal Akademisk.  ISBN 978-82-05-33505-9.  4.  s 128 - 168
• 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), s 4328- 4343 . doi: 10.1002/sim.2839
• Olsen, Bjørn Reino; Laake, Petter & Ottersen, Ole Petter (2007). Guide to grant applications, In Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (ed.),  Research Methodology in the Medical and Biological Sciences.  Academic Press.  ISBN 978-0-12-373874-5.  15.  s 433 - 456
• Parr, Christine Louise; Hjartåker, Anette; Scheel, Ida; Lund, Eiliv; Laake, Petter & Veierød, Marit Bragelien (2007). 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.
• Sexton, Joseph & Laake, Petter (2007). Boosted regression trees with errors in variables. Biometrics.  ISSN 0006-341X.  63(2), s 586- 592 . doi: 10.1111/j.1541-0420.2006.00718.x
• Svensson, Elisabeth; Hjartåker, Anette & Laake, Petter (2007). Hva skal måles og hvordan?, I: Petter Laake; Anette Hjartåker; Dag Steinar Thelle & Marit Bragelien Veierød (red.),  Epidemiologiske og kliniske forskningsmetoder.  Gyldendal Akademisk.  ISBN 978-82-05-33505-9.  2.  s 45 - 65

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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 s.
• Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (ed.) (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 s.
• Veierød, Marit Bragelien; Lydersen, Stian & Laake, Petter (ed.) (2012). Medical statistics in clinical and epidemiological research. Gyldendal Akademisk.  ISBN 9788205399594.  720 s.
• Laake, Petter; Benestad, Haakon Breien & Olsen, Bjørn Reino (red.) (2008). Forskning i medisin og biofag. 2. utgave. Gyldendal Akademisk.  ISBN 978-82-05-38487-3.  550 s.
• Laake, Petter & Valen, Guro (2008). Fra basalmedisinsk til klinisk forskning. Gyldendal Akademisk.  ISBN 978-82-05-38487-3.  14 s. 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; Benestad, Haakon Breien & Olsen, Bjørn Reino (ed.) (2007). Research Methodology in the Medical and Biological Sciences. Academic Press.  ISBN 978-0-12-373874-5.  512 s.
• Laake, Petter; Hjartåker, Anette; Thelle, Dag S. & Veierød, Marit B. (red.) (2007). Epidemiologiske og kliniske forskningsmetoder. Gyldendal Akademisk.  ISBN 9788205335059.  551 s.
• Laake, Petter; Hjartåker, Anette; Thelle, Dag Steinar & Veierød, Marit Bragelien (red.) (2007). Epidemiologiske og kliniske forskningsmetoder. Gyldendal Akademisk.  ISBN 978-82-05-33505-9.  551 s.

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• Lydersen, Stian; Fagerland, Morten & Laake, Petter (2019). Fishers eksakte test - hvordan smaker teen?. Tidsskrift for Den norske legeforening.  ISSN 0029-2001.  139(13), s 1292- 1292 . doi: 10.4045/tidsskr.19.0237 Show summary

  Et enkelt eksperiment med te og melk kan ha inspirert den britiske statistikeren Ronald Aylmer Fisher (1890–1962) til å lage en av verdens mest kjente statistiske tester.

• Lydersen, Stian; Fagerland, Morten & Laake, Petter (2019). Pearsons khikvadrattest. Tidsskrift for Den norske legeforening.  ISSN 0029-2001.  139(12), s 1183- 1183 . doi: 10.4045/tidsskr.18.0125
• Sandvig, Heidi Vihovde & Laake, Petter (2019). Ikke faglig begrunnet styrevedtak om fødesammenslåing. Dagens medisin.  ISSN 1501-4290.
• 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.
• Benestad, Haakon Breien & Laake, Petter (2015). Research Strategies, Planning and Analysis, In Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (ed.),  Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication..  Academic Press.  ISBN 978-0-12-799943-2.  Kapittel 4.  s 89 - 104
• Fagerland, Morten Wang; Lydersen, Stian & Laake, Petter (2015). Confidence Intervals for Two Independent Binomial Proportions, In N. Balakrishnan; Paolo Brandimarte; Brian S. Everitt; Geert Molenberghs; Walter W. Piegorsch & Fabrizio Ruggeri (ed.),  Wiley StatsRef: Statistics Reference Online.  John Wiley & Sons.  ISBN 9781118445112.  Leksikalsk artikkel.
• Holm, Søren; Hofmann, Bjørn & Laake, Petter (2015). Ethics and Scientific Conduct, In Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (ed.),  Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication..  Academic Press.  ISBN 978-0-12-799943-2.  Kapittel 2.  s 43 - 70
• Laake, Petter & Fagerland, Morten (2015). Statistical Inference, In Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (ed.),  Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication..  Academic Press.  ISBN 978-0-12-799943-2.  Kapittel 11.  s 379 - 430
• Olsen, Bjørn Reino; Laake, Petter & Ottersen, Ole Petter (2015). Guide to Grant Applications, In Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (ed.),  Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication..  Academic Press.  ISBN 978-0-12-799943-2.  Kapittel 15.  s 519 - 546
• Thelle, Dag Steinar & Laake, Petter (2015). Epidemiology, In Petter Laake; Haakon Breien Benestad & Bjørn Reino Olsen (ed.),  Research in Medical and Biological Sciences: From Planning and Preparation ot Grant Application and Publication..  Academic Press.  ISBN 978-0-12-799943-2.  Kapittel 9.  s 275 - 320
• Benestad, Haakon Breien & Laake, Petter (2014). Dårlig tittel - dårlig manus?. Tidsskrift for Den norske legeforening.  ISSN 0029-2001.  134(4), s 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.
• 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.
• 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), s 891- 892 . doi: 10.1002/sim.4135
• Thelle, Dag S. & Laake, Petter (2011). Fra ammetåke til klarsyn. Forskning.no.  ISSN 1891-635X.
• Karlsen, Anette; Lilleby, Wolfgang; Klein, Willibrord; Laake, Petter; Fosså, Sophie Dorothea; Eri, Lars Magne; Karlsen, Steinar; Smeland, Sigbjørn & Blomhoff, Rune (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), s 722- 723 . doi: 10.3109/00016341003657942
• Lehre, Anne- Catherine W G; Lehre, Knut Petter Dæhlin; Hansen, Arvid Hedley; Laake, Petter & Danbolt, Niels Christian (2010). Gender: Males are more extreme.
• 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. 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.

• Karlsen, Anette; Paur, Ingvild; Bøhn, Siv Kjølsrud; Sakhi, Amrit Kaur; Grethe Iren, Borge; Serafini, Mauro; Erlund, Iris; Laake, Petter; Tonstad, Serena & Blomhoff, Rune (2009). Bilberry juice modulate plasma concentration of NF- related inflammatory markers in subjects at increased risk of CVD.
• 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, s 8- 8
• Parr, CL; Hjartaker, A; Hjartåker, Anette; Laake, Petter; Lund, Eiliv; Veierod, MB & Veierød, Marit Bragelien (2009). Parr et al. Respond to "Recall Bias in Melanoma". American Journal of Epidemiology.  ISSN 0002-9262.  169(3), s 271- 272 . doi: 10.1093/aje/kwn356
• Bøhn, Siv Kjølsrud; Myhrstad, Mari Charlotte; Thoresen, Magne; Holden, Marit; Tunheim, Siv Haugen; Karlsen, Anette; Svendsen, Mette; Seljeflot, Ingebjørg; Moskaug, Jan Øivind; Duttaroy, Asim K.; Laake, Petter; Drevon, Christian A; Arnesen, Harald; Tonstad, Serena; Collins, Andrew Richard & Blomhoff, Rune (2008). Plant food phytochemicals modulate gene expression in human blood cells.
• Karlsen, Anette; Retterstøl, Lars; Laake, Petter; Paur, Ingvild; Bøhn, Siv Kjølsrud; Sandvik, Leiv & Blomhoff, Rune (2007). Anthocyanins inhibit nuclear factor-kappaB activation in monocytes and reduce plasma concentrations of pro-inflammatory mediators in healthy adults.
• Louch, William Edward; Mørk, Halvor Kjeang; Sexton, Joseph; Laake, Petter; Sjaastad, Ivar & Sejersted, Ole M (2007). Slowing of Ca2+ release in failing murine cardiomyocytes results from loss of release synchrony but not alterations in Ca2+ sparks.
• Lydersen, Stian; Laake, Petter & Fagerland, Morten (2007). Bedre hypotesetester i 2x2 tabeller. Show summary

  Når vi vil sammenlikne to binomiske andeler, eller teste for uavhengighet mellom to dikotome variable, kan dette formuleres som en test i en 2x2 tabell. Tradisjonelt benyttes Pearson’s asymptotiske kjikvadrat-test (som er ekvivalent med en to-utvalgs z-test) eller Fisher’s eksakte betingede test. Imidlertid finnes ubetingede tester som har uniformt høyere styrke enn Fisher’s eksakte test, samtidig som signifikansnivået bevares. Ubetingede tester var tidligere i praksis utilgjengelige pga at de var beregningstunge. Med dagens software kan de lett gjennomføres for små og middels store utvalg. Alternativt kan man bruke mid-p-verdien fra en betinget test. Denne beregnes ved å inkludere halve istedenfor hele punktsannsynligheten for det observerte utfallet i p-verdien. En betinget mid-p test er enkel å gjennomføre, den har bedre egenskaper enn en asymptotisk test, og prinsippet kan generaliseres til konfidensintervall. En betinget mid-p-verdi er også tilnærmet lik den tilsvarende ubetingede p-verdien. Ubetingede tester eller betingede mid-p tester bør være førstevalget ved analyse av 2x2 tabeller. Fisher’s eksakte test bør praktisk talt aldri brukes.

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