1 STAT 6020 Introduction to Biostatistics Fall 2005 Dr. G. H. Rowell Class 3

2 Ch 5: REVIEW from your Homework Students in the class will take turns defining the terms listed in this presentation that they have listed in their homework. Examples are helpful if you have them included, please mention them.

3 Ch5: Designing Research, Overview: Observational Study REVIEW

4 Ch 5: Designing Research, Overview: Experiment REVIEW

5 Ch 5: Some Definitions  Observational Study vs. Experiment  Prospective vs. Retrospective  Longitudinal vs. Cross-sectional  Control vs. Treatment REVIEW

6 Ch 5: Sources of Variation  Variation: control what you can, randomize what you cannot control  Cautions: Samples need to represent the population In comparative studies, make groups similar with respect to known sources of variation

7 Planning a Good Experiment, 2 (Cobb, Introduction to Experimental Design, Springer, 1998.)  The Content of an Experiment: 3 Decisions to Make

8 Planning a Good Experiment, 1 (Cobb, Introduction to Experimental Design, Springer, 1998.)  Three SOURCES of Variability: One We Want and Two We Don’t Want

9 Planning a Good Experiment, 1 (Cobb, Introduction to Experimental Design, Springer, 1998.)  Three KINDS of Variability: One We Want, One We Can Live With, and One That Threatens Disaster

10 Ch 5: Case Study, Section 5.4  Replicated Measures  Balanced Design  Randomization  Covariates  Sample size REVIEW

11 Ch 5: Experiment Terms  Bias (Bias vs. Chance Error)  Randomization  Blinding  Replications  Sample selection  Sample size REVIEW

12 Ch 5L Experiment Structure  See diagrams on Pages 83 – 85

13 Ch 5.7: Random Allocation  For Hand-in Homework: Name: Randomization Simulation Due Date: Monday, Sept. 19 at 9:30 AM CST Possible Points: 20 Complete the Randomization Simulation Activity found at Home.htm Be sure to submit the "pretest" and the "lesson" and the "feedback" forms. Note, there is a not a review for this lesson. Do NOT skip the "tutorial." Home.htm

14 Ch 5.7: Random Allocation  HOMEWORK: AFTER you complete the randomization simulation, read Sect. 5.7 & define Simple Randomization Block (Restricted) Randomization Stratified Randomization Cluster Randomization  Note: Skip Section 5.8 for now.

15 Ch 5.9: Observational Studies  Two Main Types of Observational Study used to investigate Causal Factors Case-Control (retrospective) Cohort (prospective)

16 Ch 5.10: Case-Control Study  Big Picture Identify group with condition (case) Identify group without condition (control) Compare past exposure to factor for the two groups  Advantage: relatively simple, quick, inexpensive, valuable with rare conditions  Disadvantage: biases can occur Homework: Read –

17 Ch 5.11: Cohort Study  Big Picture: follow-up study Identify group of subjects of interest Follow them to see what happens (Begin with unaffected observations & wait to see what happens)  Advantage: careful measurement  Disadvantage: could take a long time for a large enough proportion to be affected (expensive), not good for rare conditions  Homework: Read 5.11

18 Ch 5.12: Cross-sectional Study  All information is collected at the same time (subjects contact once) Descriptive Ex: Surveys Investigation of Associations – an alternative to the case-control and cohort approach  Advantage: no recall bias, no loss to follow-up, cheap  Disadvantage: Cannot draw clear inference of causality  Homework: Read 5.12.

19 Other Ch 5 Homework  Read Section 5.13 & 14  Work Homework Problems #  Check answers in the back of the book.