Controlling Extraneous Variables

Filysia SetiawanSusan

The Validity of a study will be approached from four

perspectives

Environmental IssuesGrouping IssuesPeople IssuesMeasurement Issues

Environmental Issues

Naturally occurring variables Environmental situation naturally will affect the variables although it is indirectly.

Environmental Issues

Artificiality is surreptitiously alter the intentions of a study. Artificiality Experimental miceIn which the conditions are artificial, as they would in the real world

Grouping Issues Self – selectiongenerally refers to the practice of letting the subjects decide which group to join.

Mortality refers to students who self-select themselves out of group by dropping out of the study for any number of reasons.

Grouping Issues

Maturation Different individuals can have

different experiences that cause them to mature or change over time.

People Issues

Hawthorne effectit happens if the result of investigation are more closely related to this pleasure than to anything that actually occur in the research.

Halo effect is due to the tendency among human beings to respond positively to a person they like.

People Issues

Subject expectancyoccurs when the subjects think they have figured out what study is about.

People Issues

Researcher expectancyas Rosenthal showed can be a

problem in behavioral research.Is often controlled for with double

blind technique in medical research.

Measurements IssuesPractice effect essentially involves the potential

influence of the measures on each otherReactivity effectmay occur when this measures

themselves are causing a change in the subjects.

Measurement Issues

Instability of measures and resultsrefers to the degree to which the result on the measure are consistent.

ConclusionPerspectives Potential Problems Steps toward control

Environmental Natural Variables

Prearrangement of conditions

Artificiality Approximation of natural conditions

Grouping Self-selection Random, matched-pair, or stratified assignments

Mortality Short duration, track down missing subject

Maturation Short duration or built-in moderator or control variables

ConclusionPerspectives Potential Problems Steps toward control

People Hawthorne effect Double-blind techniqueHalo effect Built-in general attitude

as moderator or control variables

Subject expectancy Minimize obviousness of aims. Distraction from aims provided

Researcher expectancy Double –blind techniqueMeasurement Practice effect Counterbalancing

Reactivity Careful study of measuresInstability of measures and results

Statistical estimates of stability and probability