Operational definition=specifies operations/procedures used to produce/measure something, ordinarily a way to give it numerical value. 9/16/15: not dictionary definition, how to measure something. Need to worry about unusual ppl in studies. Convenience sample=group chosen bc ease of study. Representative sample=big improvement over convenience sample; resembles pop. Random sample=better; every individual in pop. has = chance of being selected: larger smaller probability that results differ substantially from whole pop, difficult. Cross-cultural sample=groups of ppl from @ least 2 cultures: difficult bc of expense, language barriers, and reluctance of ppl. Naturalistic observation: careful exam. of what happens under >/< natural conditions: case history=thorough description of person, including abilities/disabilities, medical condition, life history, unusual experiences, and other relevancies. Psychologist who encounters someone w/rare condition may report one. Survey=study of prevalence of certain beliefs, attitudes, or behaviors based on ppl"s responses to q"s: results can be misleading, wording of q"s changes connotation, someone can bias answers by rewording q.