This document discusses control in developmental research methods. It explains that control is established through careful selection of participants and random assignment to conditions. Random assignment balances any differences between groups to minimize confounding variables. True experiments use both random selection and assignment to control for threats to internal validity like history, maturation, and testing effects. Different experimental designs, like the Solomon four-group design, allow researchers to rule out additional validity threats.

1. Developmental Research
Methods
Topic 7: Control
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2. Control through selection
 First step in making our experiment
internally valid
 Selection
◦ Who to select?
◦ How?
◦ Must be representative
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3. Simple Random Sampling
 Population
 Randomly select
 Fair?
 Representative
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4. Random assignment
 Balances 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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5. Experimental design control
 Design allows us to detect cause
 We are all about ruling out confounds.
 Not all designs created equal
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6. True Experiments
 True experiments
◦ Random selection and
random assignment
◦ Controls for most threats
to internal validity
 History, maturation,
selection, testing, etc.
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7. 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 effects
R 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 effects
R 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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8. Credits
 www.sxc.hu
◦ Gears
◦ Beakers – 123dan321
◦ Puzzle – lusi
 Minions – Illumination Entertainment
 People – Ryan Sain
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