Nature vs nurture debate and interactions (twin studies: fraternal vs paternal) Hypothesis what i expect to find based on clinical evidence or theory. Research design types of research, population, variables. Qualitative ethnography, case study/focus group, phenomenology, grounded theory. Quantitative descriptive, quasi-experimental, experimental, program evaluation. Experimental and quasi-experimental studies: longitudinal, cross sectional, single subject repeated measurement in controlled situation, own performance is compared; rigorous approach to controlling variables, clinical studies placebo controlled, action research. Only one variable is manipulated and tested. Cause and effect requires a timeline of events. Involved manipulation of iv and observation of its effects on dv. Control groups: placebo effect, placebo control groups, double blind control. Face validity: does it appear to measure what it measures. Criterion validity: how well the instrument compares to another. External validity: how well can it be generalized. Internal: consistent with itself; how well is the study measuring inferences regarding cause- effect or causal relationships.