04/10/2023 CEDP321 Ryan Sain, Ph.D. 1

Developmental Research MethodsTopic 7: Control

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Control through selectionFirst step in making our

experiment internally valid Selection

◦Who to select?◦How?◦Must be representative

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Simple Random Sampling Population Randomly select Fair? Representative

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Random assignmentBalances differences that we

didn’t control for through selection.

This minimizes confounds – or at least makes the equally likely to occur in both groups

But it doesn’t get rid of them◦It’s entirely possible that all females

end up in one group◦Just makes it unlikely

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Experimental design controlDesign allows us to detect causeWe are all about ruling out

confounds.Not all designs created equal

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True ExperimentsTrue experiments

◦Random selection and random assignment

◦Controls for most threats to internal validity History, maturation,

selection, testing, etc.

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Selection process

Group Measurement IV level Measurement

- Group A - Treatment DV

No ability to detect cause

(r) Experimental - Treatment DV

(r) Control - No Treatment DV

Starting to detect cause, but we’re not sure about natural change (only one measure) and random effectsR Experimental Pretest Treatment Posttest

R Control Pretest No Treatment posttest

Now we are able to start detecting changes within each group over time (2dv) to allow for measurement of maturation effectsR Exp 1 Pretest Treatment Posttest

R Control 1 Pretest posttest

R Exp 2 Treatment posttest

R Control 2 Posttest

The solomon 4 group – rules out maturation, testing, and selection effects

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Creditswww.sxc.hu

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