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Basic Biostatistics

Basic Biostatistics. Prof Paul Rheeder Division of Clinical Epidemiology. Overview. Bias vs chance Types of data Descriptive statistics Histograms and boxplots Inferential statistics Hypothesis testing: P and CI Comparing groups Correlation and regression. Research Questions?.

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Basic Biostatistics

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  1. Basic Biostatistics Prof Paul Rheeder Division of Clinical Epidemiology

  2. Overview • Bias vs chance • Types of data • Descriptive statistics • Histograms and boxplots • Inferential statistics • Hypothesis testing: P and CI • Comparing groups • Correlation and regression

  3. Research Questions? • Does CK level predict in hospital mortality post MI? • Is there an association between troponin I and renal function? • What is the Incidence of amputation in diabetics with renal failure? HOW ARE THEY MEASURED???

  4. Research question • Does aspirin reduce CV mortality in diabetics when used for primary prevention? • Is there an increased risk between cell phone use and brain cancer? • Does level of SES correlate with depression?

  5. Research question • So your research question must be phrased in such a manner that you can answer YES or NO or provide some quantification of sorts.

  6. Data analysis • Aim: to provide information on the study sample and to answer the research question !

  7. Problems !

  8. Problems • Bias and confounding also called systematic error…. Typically dealt with in the planning and execution of the study…can also control for it in the data analysis (eg multivariate analysis) • Chance also called random error. Classically P values (and CI) can be used to judge role of chance

  9. First important issues • What type of data are you collecting • Typically one has some outcome variable and some exposure variable or variables? • How and with what are they measured?

  10. Outcome and exposure? • Does CK level predict in hospital mortality post MI? • Is there an association between troponin I and renal function? • What is the Incidence of amputation in diabetics with renal failure? HOW ARE THEY MEASURED???

  11. Research question • Does aspirin reduce CV mortality in diabetics when used for primary prevention? • Is there an increased risk between cell phone use and brain cancer? • Does level of SES correlate with depression?

  12. Research question • So your research question must be phrased in such a manner that you can answer YES or NO or provide some quantification of sorts.

  13. Types of data • Categorical: HT yes or no, sex, smoking status (usually a %) • Ordinal versus nominal • Continuous data • Spread of continuous data

  14. Data analysis • Descriptive stats • Mean/median • SD or range

  15. Hypothesis testing • Differences between groups: • Examples: • T test/Mann Whitney (2 groups) • ANOVA/ Kruskal Wallis (>2 groups) • Chi square if it is %

  16. Associations between variables • Does coffee cause cancer (OR, RR) • Efficacy of Rx (RRR, ARR, NNT) • If BMI associated with BP (correlation and regression)

  17. 2 X 2 table RR= (a/a+b)/(c/c+d) OR = (a/b)/(c/d)

  18. TYPES OF DATA

  19. DESCRIPTIVE STATS

  20. Graphics

  21. Using the SD and the Normal Curve

  22. Mean ± 1.96 SD = 95% range of sample • Mean ± 1.96 SEM=95% Confidence interval

  23. One of many samples

  24. 95% Confidence Intervals

  25. Hypothesis Testing

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