Diffusion of responsibility- each person feels decreased personal responsibility for intervening. Variable- any characteristics that can differ: memory personality, gender, intelligence, stress, learning, and motivation. Operational definition- variable in terms of the specific procedures used to produce or measure it: translate an abstract term into something observable and measureable, must measure it. Physiological measures: physiological functioning helps understand a persons mind. Heart rate, blood pressure, respiration rate, hormonal secretion, electrical and biochemical processes in the brain: have interpretive problems that we don"t always understand. Descriptive methods: identify how humans and other animals behave, usually in natural settings, case studies, naturalistic observations, surveys, case study- in-depth analysis of an individual, group, or event. Gathered through observations, interviews, psychological tests, physiological recordings, and task performance. Advantages: study it intensively and collect large amounts of data, may challenge validity of a theory or widely held belief. Illustrate effective intervention programs developed by clinical psychologists to treat special populations.