Extraneous Variables

Controlling Extraneous Variables Environmental issues Naturally occurring variables: usual with several groups of people • Noise • Temperature • Light • Time of day • Seating arrangements Artificiality: Classroom or Office are not “real world” or “natural” Using a recording device or a camera

People act differently when they are aware they are being observed

People change attitudes and actions when social situation changes People often want to please and be praised People are influenced by physical environment and personal physical state People bring emotional states caused by extraneous factors

Self-selection: let subjets decide which group to join • Volunteers: different from the outsed, more highly motivated • Two class sections could have wide differences Mortality (attrition, dropout): Students elect to leave a group: leaves slant toward more motivated Maturation: studies conducted over longer period must account for changes in group and individuals

People Issues Hawthorn Effect: pleasure of being included in the study enhances performance Halo Effect: people respond well to those whom they like. Subject Expectancy: people tend to want to please Researcher Expectancy: Subtle and uncontrolled attitude toward subjects: like high performers, dislike low performers

Measurement Issues (Results are only as good as the data.) Measures (tests, questionnaires, interviews) should not introduce extra variables Practice Effect: same test given repeatedly Reactivity Effect: attitude surveys form or solidify attitudes in response to survey Instability of Measures and Results: degree to which results likely to recur if study is replicated

Controlling for Validity Logic = internal validity Meaningfulness = external validity Control extraneous variables • Environmental issues: comfortable • Grouping issues (avoid volunteer grouping): take steps to assure that the group is representative and equivalent • Short-term study avoids maturation • People issues: • try to find a double-blind technique • Minimize obviousness to subjects • Control expressions of attitude • Measurement issues: • Counterbalancing: no individual takers of the same test more than once • Reactivity: question subjects and gauge thought processes

Control versus Generalizability If two or more uncontrolled extraneous variables also influence each other… Example: Researcher expectancy can trigger subject expectancy, creating a practice effect. INTERNAL VALIDITY (Logic): results due solely to variables identified and compared. EXTERNAL VALIDITY (Meaningfulness): Factors affect generalizability of study to real world, i.e. artificiality.

1. Purpose: purpose of experimental research is to study cause-andeffect relationships between two variables, whereby the causal variable can be manipulated. 2. Hypothesis: Stated at the beginning of the study. 3. Data Collection/Sources: quantitative data from test scores, attitudinal surveys and other measurements. Researcher controls for internal validity. 4. Data Analysis: data are coded and converted into an electronic format and analyzed using a computer software program such as SPSS. Researcher can use any number of analytical processes. Differences in rwo or more groups using t tests and analysis of variance. 5. Reporting Results: brief, clear and to the point. Description of methodology and procedural controls. Results of data analysis presented. Can infer external validity if threats to external validity were controlled.