Research Design Classification

1. NTR 629 - Week 2 Research DesignClassification

2. How Study Designs Differ • Number of observations made • Directionality of exposure • Data collection methods • Timing of data collection • Unit of observation • Availability of subjects

3. Study Design Approaches Experimental Approaches Observational Approaches No manipulation No randomization of study subjects/units Less rigorous than experimental designs Analytic or descriptive Analytic studies E.g., many ecologic studies, case-control studies, cohort studies Descriptive studies: E.g. cross-sectional surveys • Manipulation (exposure of interest controlled by the investigator) • Hypothesis testing • Examines cause-effect • Quantitative and analytic • Experimental Design • Most rigorous design. Randomization of study subjects/units • Quasi-experimental Design • Less rigorous, because no randomization of study subjects/units

4. Classification Based on Purpose Analytical Descriptive Case Study Case Series Developmental Correlational Descriptive Survey Field/Ethnographic • Experimental • Quasi Experimental • Pre-Experimental • Cohort studies • Case Control (or Single Subject) • Historiography • Analytical Survey • Content Analysis • Causal-Comparative

5. Design Characteristics Analytical Descriptive No true hypothesis Establishes a relationship Describes state of nature at point in time No control of variables Recording of observations Primarily to totally qualitative • Test hypothesis • Allows detection of causal associations • Numerical data – quantitative.

6. Analytical Designs (Part 1):Experimental Designs

7. True Experimental Design • Pretest post-test control group design • TWO (or more) groups: • Random/control group O1 O2 • Random/experimental group O1 X O2 • Caution with within-session variation between treatments A and B… control conditions. Pretest important if need to check equivalence of groups. • Key for Study Design Symbols: • O1 = observation 1 (measurement of dependent variable) • X = manipulated variable; independent variable • O2 = observation 2 (measurement of same dependent variable as O1)

8. True Experimental Design • Pretest post-test control group design • THREE groups: • Random/control group O1 O2 • Random/experimental group A O1 XA O2 • Random/experimental group B O1 XB O2 • Caution with within-session variation between treatments A and B… control conditions. Pretest important if need to check equivalence of groups.

9. True Experimental Design • Post-test only control group design • TWO (or more) groups: • Random/control group O2 • Random/experimental group X O2 • No pretest? Assume equivalence with randomization. No interaction effect with pretesting.

10. True Experimental Design • Solomon four group design • FOUR groups: • Random/experimental group O1 X O2 • Random/control group 1 O1 O2 • Random/control group 2 X O2 • Random/control group 3 O2 • Important if taking pretest influences post-test.

11. Quasi Experimental Design • Nonequivalent control group design • TWO groups: • Experimental group O1 X O2 • Control group O1 O2 • Uses intact groups (e.g., class); no randomization

12. Quasi Experimental Design • Static group design • TWO groups: • Experimental group X O2 • Control group O2 • Uses intact groups (e.g., class); no randomization

13. Quasi Experimental Design • Counterbalanced design • FOUR (or more) groups (A, B, C, D) and FOUR (or more) treatment variations (1, 2, 3, 4), with exposure at different times during study: • Replication Treatment Variations XA XB XC XD 1 A B C D 2 B D A C 3 C A D B 4 D C B A • Uses intact groups (e.g., class); no randomization

14. Quasi Experimental Design • Single subject design • ONE subject: • Experimental subject base-O1 X withdraw-X O2 • “Behavioral”, natural setting, little generalizability

15. Quasi Experimental Design • One group time series design • ONE group: • Experimental group O1 O2 O3 O4 X O5 O6 O7 O8 • Determine if effect of X, and if X is short-term effect.

16. Quasi Experimental Design • Control group time series design • TWO groups: • Experimental group O1 O2 O3 O4 X O5 O6 O7 O8 • Control group O1 O2 O3 O4 O5 O6 O7 O8 • Helps control selection-maturation effects.

17. Quasi Experimental Design • Control group time series design • FIVE (or more) groups: • Experimental group A O1 X O2 • Experimental group B O1 X O2 • Experimental group C O1 X O2 • Experimental group D O1 X O2 • Experimental group E O1 X O2 • Helps control maturation, pretest, regression, history

18. Factorial Design • 2x2 factorial design • To examine interaction effects of two or more independent variables (X) and test several H0 simultaneously. Teaching method (X1)Length of period (X2) 50 minutes 30 minutes • Discussion O1 O2 • Lecture O3 O4

19. Factorial Design • There are many variations of factorial designs. The variables can have multiple levels. E.g.,: • 2x3 design • two X (X = manipulation): one with two levels, one with three levels • 3x3 design • Three X, each with three levels • 2x2x2 design • Three independent variables, each varied two ways

20. Controlled Clinical Trials Advantages Limitations Artificial setting Limited scope of potential impact Adherence to protocol is difficult to enforce Possible ethical dilemmas • Experimental Design • Comparing outcomes in treated group compared to an equivalent control group • Participants in both groups are enrolled (random assignment into group), treated, and followed over the same time period • Single or double-blinded. • Used to test efficacy of preventive (prophylactic) or therapeutic (curative) measures • Multicenter trials--results from several researchers pooled.

21. Schematic Diagram of a Clinical Trial SAMPLE Nonparticipants Randomization to groups Intervention group Control group Lost to follow-up Measure outcome Measure outcome

22. Clinical Trial Crossover Designs • Any change of treatment for a patient in a clinical trial involving a switch of study treatments. • Planned crossovers • Protocol is developed in advance, and the patient may serve as his or her own control. • Unplanned crossovers • Exist for various reasons, such as patient’s request to change treatment. • Members of both groups receive both treatment regimens • Group 1 receives treatment A then treatment B • Group 2 receives treatment B then treatment A Treatment A Treatment B

23. Community Trials Advantages Limitations Inferior to clinical trials with respect to ability to control entrance into study, delivery of the intervention, and monitoring of outcomes. Fewer study units are capable of being randomized, which affects comparability. Affected by population dynamics, secular trends, and nonintervention influences • Represents the only way to estimate directly the impact of change in behavior or modifiable exposure on the incidence of disease. • Community intervention trials determine the potential benefit of new policies and programs. • Community refers to a defined unit, e.g., a county, state, or school district.

24. Community Trials - Steps • Community trials start by: • Determining eligible communities and their willingness to participate • Collect baseline measures of the problem to be addressed in the communities, e.g., disease rates, knowledge, attitudes, and practices • Communities are randomized (intervention and control) • Followed over time • Outcomes of interest are measured