1. Typing error 2. Logic, reasoning Logic of scientific work ... - medri

Logical Principles of Reserch inMedicine with Most Common Errors1. Typing errorLogical Principles of Research inMedicine with Most Common ErrorsFrom Idea to Publicationa ☺Prof. Mladen Petrovečki, MD, PhDPh.D. Programe Biomedicine & Health ScienceZagreb University School of Medicine2010/112. Logic, reasoningLogic of scientific work1. rules of logic and logic itself as a way of validthinking is more expressed in science andphilosophy compared to other humanactivities…2. science is recognized by utilizing empiricalmethods and therefore logic is prerequisite inscientific methodology...www.glasbergen.com/Mirko Jakić. Logika. Školska knjiga, Zagreb 2003.Logic of scientific work3. use of is logic evident in using logicalreasoning, by using terms such as rules,conclusions, definitions, distributions, proves,etc.4. logic – how our thinking is valid in ourmission to find the truth…3. Nonscientific procedures• diligence(habit, attitude, manner, believe, momentum)• authority• intuition1

4. Argument, proof 5. Logic in science• system• models of the system• deterministic• probabilistic• event probability → P(E)0 ≤ P(E) ≤ 16. Probability• mathematical calculation that something, event,will occur• mathematic probability theory• statistics• mathematics• scientific methodology• logic, philosophy• reasoning about event feasiblenessProbability, calculation• symbol – P• No. of expected eventsP =No. of all events• values range 0 – 1:• 0 – impossible event• 1 – certain eventProbability, the term• probability• vjerojatnost, mogućnost• possibility• mogućnost, vjerojatnost, izvedivost• likelihood• vjerojatnost, mogućnost• chance• mogućnost, prigoda, slučaj, slučajnost, vjerojatnost, sreća,povoljna prilika• odds• izgled, prednost, vjerojatnost, slučajnost7. Statistics• probability calculation• probabilistic modelof the system2

Statistical mechanics8. Measuring & 9. Research• Lord Kelvin(1824.-1907.)• James C. Maxwell(1831.-79.)• Ludwig Boltzmann(1844.-1906.)• Willard Gibbs(1839.-1903.)populationknowledge about population ≠ ≠ ...variablep = ?10. Variable• all variables in research11. Measuring scalesNOMINAL• as many of them• the end of research• simple → complex (data)• accuracy (numbers)• measuring scalesORDINALRATIOINTERVAL12. Error13. Populationknowledge on populationpopulationvariableSAMPLINGsystematicincidentalsampleknowlede on samplestatistical dataanalysis3

14. Sample• part of population• what? who?• when?• where?• sizeSample• representative• measurable• probabilistic• simple• system• stratified• clusterSample15. Samplingrelatedunrelatedwww.statehousereport.comSamplingMedCalc16. Bias (sampling)4

Bias (sampling)17. Blinding• Bias – systemic sampling error• prevalence bias (Neyman)• admittance rate bias (Berkson)• answering rate bias• etc.• single-blind• double-blind• triple-blind• quadruple-blind18. Control group• must have• to be compared with experimental group• Hawthorn effect• research with no control group• subject changes behavior with a knowledge thatis a part of experiment• subject feels better with knowledge to be a part ofexperiment19. Hypothesishttp://biology.ucf.edu/~pascencio/images/Hypothesis.jpg20. Statistical hypothesisStatistical hypothesiselemental statementtruth or not (false, lie)hypothesis testing → finding the truthtruth real object stateprobabilistic system:truth → probabilitysignificant any occasion other thataccidentally:probability → level of significance5

21. Null-hypothesisNull-hypothesisNo differenceNo difference ≈ Not guilty22. Testing the hypothesisA. null-hypothesisB. statistical testC. level of significanceD. statistics calculationE. conclusionA. Hypothesis• null – H 0 – no difference• alternate – H 1 – difference exists• only one can be truthful• only one can be accepted, other will berejectedB. Choosing the test• measuring scales• sample• size• related on unrelated samples• data distribution• parametric• nonparametric• no. of variables• etc.23. Statistical testsScale One sample Two Three or morerelated unrelated related unrelatedNominal binomial McNemar Cohranchi-square Fisher chi-sqr.chi-square/Ordinal Kol.-Smirn. Wilcoxon FriedmanMWp/medianMosesKWInterval ...Ratio ...6

C. Level of significance24. Statistical errors• Pα if defined before statisticsα – probability of rejecting H 0 when H 0 = truth• error α (type I error or false positive error)• as less as possible• default values, e.g. P 0,0526. Conclusion (E)• low P low possibility to reject the truth• conclusion:• P < α• low probability that H 0 is true• reject (not accept) null hypothesis• accept alternate hypothesis• statement “...” is truth with P = ...27. Yes & No in statistics• hypothesis = ?• calculation = ?• correct data = ?• all conditions for statisticvalid = ?• no limitations = ?7

Example 1: “Not” in correlation(cont.)yyyxxxN r plinear 118 0,25 0,006logarithm 118 0,43

30. The truthProf. dr. Mladen PetrovečkiDepartment of Medical InformaticsRijeka University School of Medicinehttp://mi.medri.hrDepartment of Clinical Laboratory DiagnosisImmunology DivisionDubrava Clinical Hospital, Zagrebwww.kbd.hr/lab mladenp@kbd.hr9