Quasi-experimental designs and ex post facto designs exam with 100% correct answers already graded A+

What is an ex post facto design? An ex post facto research design is a method in which groups with qualities that already exist are compared on some dependent variable. ... The assignment of subjects to different groups is based on whichever variable is of interest to the researchers Pre-experimental designs No control groups and no random assignment of subjects to conditions. Acceptable for pilot research, other avoid at all costs Experimental designs Control group(s), random assignment of subjects to conditions Quasi-experimental designs Often control groups, but no random assignment of subject conditions. What are issues with quasi experimental designs? They do not fill the requirements for a true experimental (analytic) experiment - Internal validity issues - External validity issues - No random assignment possible When are within subject designs useful? Useful when statistical power is an issue Useful when few measurements are possible Useful when availability of participants is limited. Typically, random assignment is not possible A common mistake the "pooling" fallacy What is the pooling fallacy? Problems Arising when Individuals Contribute More than One Observation to the Data Set Solution for order effects Counterbalancing Ex: melatonin effect with jet lag How do you measure order effects? Make the orders in factors Our experiment becomes a 2x2 IN ex post facto designs the research arrives _______ After the fact "_______" has implemented the treatment Nature i.e., Groups are based on natural occurrences that make them distinct, different Invasive research: does chronic stress predisposes to cancer? Compare people in high stress jobs to people with low stress jobs and follow them in a longitudinal study Or Find people with cancer and people without cancer and investigate their path (last ten years) What is a prospective ex post facto design? (cohort design) Finding cause and then effect. So people in high stress jobs vs low stress jobs, see if that causes cancer What is a retrospective ex post facto design? Effect --> Cause Comparing the lifestyles of people with cancer to healthy people to determine a cause Characteristics of EFP designs Participants are selected after the fact Two main reasons: - ethics - Subject variables become independent variable and are treated as treatment conditions Why do subject variables become independent variables? You cannot randomly assign people to different age groups, genders, etc, as those labels already define them as subjects Internal validity issues 1 for prospective EPF designs NO random sampling from population No random assignment to conditions Confounded variables typical to the groups investigated ex: high stress jobs participants smoke and drink more selection of subjects becomes complicated and strict criteria must be applied Convenience sampling is problematic. The sampling criteria may themselves be confounds. Prospective EPF designs: internal validity issues 2 Detection bias: common in biomedical/health research Prospective EPF designs: external validity issues Choice of groups: air traffic controllers, versus search and rescue technicians, versus crab fishermen, etc.. - Can we generalize from one group (occupation) to the other? Do the ATC people represent well the "high stress jobs?" - Does the choice of "high stress jobs" represent well "people with chronic stress" -Does occupational stress differ from "domestic/personal stress?" The issue of experimental mortality or attrition What is experimental mortality? What is a prospective EFP design solution? Matching