Measuring variables and the degree of association between them. Enables researchers to study naturally occurring variables, including variables that would be too difficult or unethical to manipulate. Random assignment to conditions and control over the events that occur; determining the effects of manipulations of the independent variable(s) on changes in the dependent variable(s) True experiments: examine cause and effect relationships, 2 essential characteristics: Control over the experimental procedures (e. g. , manipulate iv) Random assignment (aka, great equalizer: assigning participants to conditions of your experiment in such a way that every participant has an equal chance of being assigned to any of the conditions of the study. Assigning participants to conditions of your experiment in such a way that every participant. Choosing participants for your study in such a way that every member of the population of interest has has equal chance of being assigned to any of the conditions of the study.