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

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### STAT 6020Introduction to BiostatisticsFall 2005Dr. G. H. Rowell

Class 3

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.

Ch 5: Some Definitions

- Observational Study vs. Experiment
- Prospective vs. Retrospective
- Longitudinal vs. Cross-sectional
- Control vs. Treatment

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

Planning a Good Experiment, 2(Cobb, Introduction to Experimental Design, Springer, 1998.)

- The Content of an Experiment: 3 Decisions to Make

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

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

Ch 5: Case Study, Section 5.4

- Replicated Measures
- Balanced Design
- Randomization
- Covariates
- Sample size

Ch 5: Experiment Terms

- Bias (Bias vs. Chance Error)
- Randomization
- Blinding
- Replications
- Sample selection
- Sample size

Ch 5L Experiment Structure

- See diagrams on Pages 83 – 85

Ch 5.7: Random Allocation

- For Hand-in Homework: Name: Randomization SimulationDue Date: Monday, Sept. 19 at 9:30 AM CSTPossible Points: 20Complete the Randomization Simulation Activity found athttp://mtsu.edu/~smcdanie/I_cubed/Lesson2/lesson2-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."

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.

Ch 5.9: Observational Studies

- Two Main Types of Observational Study used to investigate Causal Factors
- Case-Control (retrospective)
- Cohort (prospective)

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 5.10.1 – 5.10.6

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

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.

Other Ch 5 Homework

- Read Section 5.13 & 14
- Work Homework Problems # 1 -3.
- Check answers in the back of the book.

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