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- 1. BASIC BIOSTATISTICS Diane Flynn, LTC, MC Colin Greene, LTC, MC
- 2. Objectives Overview of Biostatistical Terms and Concepts Application of Statistical Tests
- 3. Why Use Statistics? Descriptive Statistics • identify patterns • leads to hypothesis generating Inferential Statistics • distinguish true differences from random variation • allows hypothesis testing
- 4. Why Use Statistics? Cardiovascular Mortality in Males 0 0.2 0.4 0.6 0.8 1 1.2 '35- '44 '45- '54 '55- '64 '65- '74 '75- '84 SMR Bangor Roseto AJPH 1992
- 5. Types of Data Numerical • Continuous • Discrete Categorical • Ordinal • Nominal
- 6. Descriptive Statistics Identifies patterns in the data Identifies outliers Guides choice of statistical test
- 7. Percentage of Specimens Testing Positive for RSV Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun South 2 2 5 7 20 30 15 20 15 8 4 3 North- east 2 3 5 3 12 28 22 28 22 20 10 9 West 2 2 3 3 5 8 25 27 25 22 15 12 Mid- west 2 2 3 2 4 12 12 12 10 19 15 8
- 8. Descriptive Statistics Percentage of Specimens Testing Postive for RSV 1998-99 0 5 10 15 20 25 30 35 Jul Sep Nov Jan Mar May Jul South Northeast West Midwest
- 9. Describing the Data with Numbers Measures of Central Tendency • MEAN -- average • MEDIAN -- middle value • MODE -- most frequently observed value(s)
- 10. Distribution of Course Grades 0 2 4 6 8 10 12 14 Number of Students A A- B+ B B- C+ C C- D+ D D- F Grade
- 11. Describing the Data with Numbers Measures of Dispersion • RANGE • STANDARD DEVIATION • SKEWNESS
- 12. Measures of Dispersion • RANGE • highest to lowest values • STANDARD DEVIATION • how closely do values cluster around the mean value • SKEWNESS • refers to symmetry of curve
- 13. Measures of Dispersion • RANGE • highest to lowest values • STANDARD DEVIATION • how closely do values cluster around the mean value • SKEWNESS • refers to symmetry of curve
- 14. Standard Deviation σB σA Curve B Curve A
- 15. Measures of Dispersion • RANGE • highest to lowest values • STANDARD DEVIATION • how closely do values cluster around the mean value • SKEWNESS • refers to symmetry of curve
- 16. Skewness Curve A Curve B negative skew Mode Median Mean
- 17. The Normal Distribution Mean = median = mode Skew is zero 68% of values fall between 1 SD 95% of values fall between 2 SDs . Mean,Median,Mode 1 σ 2σ
- 18. Inferential Statistics Used to determine the likelihood that a conclusion based on data from a sample is true
- 19. Terms p value: the probability that an observed difference could have occurred by chance
- 20. Hypertension Trial DRUG Baseline mean SBP F/u mean SBP A 150 130 B 150 125
- 21. Terms confidence interval: The range of values we can be reasonably certain includes the true value.
- 22. 30 Day % Mortality Study IC STK Control p N Khaja 5.0 10.0 0.55 40 Anderson 4.2 15.4 0.19 50 Kennedy 3.7 11.2 0.02 250
- 23. 95% Confidence Intervals -.40 -.35 -.30 -.25 -.20 -.15 -.10 -.05 .00 .05 .10 .15 .20 Khaja (n=40) Anderson (n=50) Kennedy (n=250)
- 24. Types of Errors No difference Difference No difference TYPE II ERROR (β) Difference TYPE I ERROR (α) Truth Conclusion Power = 1-β
- 25. What Test Do I Use? 1. What type of data? 2. How many samples? 3. Are the data normally distributed? 4. What is the sample size?

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