Applied Research Methods

Applied Research Methods - ESP 178 Applied Research Methods...

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ESP 178 Applied Research Methods 2/6 Lecture: Experiments Key Concepts from Chapter 7: Experiments: greater confidence in the validity of causal conclusions than is possible in other research designs – rate well on all criteria for internal validity (see Chapter 6). 1. Experimental and comparison groups (to establish association) Group Definition Example Experimental or treatment group Group of subjects who receive “treatment” Families living on cul-de-sacs Comparison or control group Group of subjects to whom experimental group can be compared – exposed to different treatment (or no treatment) or has different value on the independent variable Families not living on cul-de-sacs 2. Pretest and Posttest measures (to establish time order) Test type Definition Example Pretest Measures dependent variable prior to treatment in both groups; not always done. Survey of street play before families move to cul-de-sac Posttest Measurement of dependent variable in both groups after experimental group has received treatment; always done in true experiments. Survey of street play after families move to cul-de-sac 3. Randomization (to establish nonspuriousness) Approach Definition Example Random assignment Start with one group, randomly assign individuals to experimental and control groups; removes bias but differences based on chance; useful for internal validity but not generalizability. Take a sample of families, randomly assign them to living on a cul-de-sac or not living on a cul-de-sac Matching Match individuals in treatment group with individuals in comparison group by pairing individuals based on selected characteristics (e.g. age, gender, etc.); not as good as random assignment Find a sample of families moving to cul-de-sacs; find families not moving to cul-de-sacs that match on number of children, age of children, income Types of Experiments Type Key Features Independent Variable Example Experimental True experiment Two comparison groups; variation in independent variable before assessment of change in dependent variable; random assignment to comparison groups Treatment or intervention,
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Applied Research Methods - ESP 178 Applied Research Methods...

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