Based on logic and common sense, not arbitrary: 3 major types of scientific research. Naturalistic observation obs of ppl or animals in their natural environment. Clinical observation the observation of the behaviour of ppl who are undergoing diagnonsis or treatment. Least formal and constrained by fewest rules. Provide foundations of biological and social sciences. Correlation studies obs in nature, but involve more formal measurement, of environmental events of individuals" physical and social charac, and of their behav. Examination of relations btwn 2+ measurements of behav or other charac of ppl/animals. Experiments go beyond measurement; make something happen and obs results. Only thing that can positively identify the causal relations among events. Study where indep variable can be changed and observe whether manipulation affects value of depen variable. Only thing tht can confirm the existence of cause-and-effect relations among. Provide general accounts of phenomena stumbled upon. Sird stereogram some ppl take longer than others to identify hidden variables objects in images.