Research psych 10

internal validity

Generally, what is the main priority for experimental studies?

the number of levels of the independent variable participants are exposed to

What is the primary difference between pretest/posttest designs and within-groups designs?

occurs when experimenters allow participants to choose their own treatment group.

Which of the following is true of selection effects?

systematically

A threat to internal validity occurs only if a potential design confound varies with the independent variable

concurrent-measures design

A design in which participants are exposed to all the levels of an independent variable at roughly the same time and a single attitudinal or behavioral preference is the dependent variable is known as a(n)

These designs rely on fewer participants

Which of the following is an advantage of within-groups designs?

they require fewer participants

One reason researchers use within-group designs is…

how experiment makes casual claims

covariance, temporal precedence, internal validity

Covariation

Differences in the measured dependent variable (DV) across experimental conditions indicate an association between the IV and DV.

Design confound

unintended variable that changes systematically alongside the independent variable, creating an alternative explanation for the results

Systematic Variability

identifiable factor that consistently affects the measured outcome

Unsystematic Variability

random or unpredictable differences that are not consistently associated with experimental conditions

Standardization

Preventing Design Confounds, Researchers keep procedures and other relevant factors consistent across experimental conditions.

Random Assignment

Controlling Preexisting Group Differences

Selection effects

when participants in different experimental groups have preexisting differences that could explain differences in the dependent variable (threatens internal validity)

Matched-group designs

match participants on relevant characteristics before assigning them to conditions

Matching

helps make experimental groups more comparable on characteristics related to the DV; reduces the likelihood that differences in those characteristics explain the results; can be especially useful when sample sizes are small

Independent-Groups Design

Between-Subjects Design

posttest-only and pretest/posttest

Independent-Groups Design types

Posttest-only design

The DV is measured only after the experimental manipulation. (cannot see what happens before, but only need to be conducted once)

Pretest/posttest design

The DV is measured both before and after the experimental manipulation (allows to measure change in a individual over time, may influence the participants performance)

Within-Groups Design

Within-Subjects Design, (dependent group design)

concurrent-measures and repeated measures

within-groups design types

repeated measures design

participants are measured on the DV more than once, after exposure to each level of IV

concurrent measures design

participants exposed to all levels at the same time, single preference measured

Practice effects

repeated testing may improve performance independently of the intervention

order effects, practical limitation, demand characteristics

disadvantage of within-group design

order effects

Responses may change depending on the order in which participants experience the conditions.

Practical limitation

Some treatments produce permanent or long-lasting changes, making it impossible to return participants to their original state. (learning to ride a bike)

Demand Characteristics

Participants may recognize the study's purpose after experiencing multiple conditions. (note-taking methods)

Counterbalancing

presenting experimental conditions in different orders across participants to reduce systematic bias caused by order effects

full counterbalancing

every possible order is used

partial counterbalancing

only some orders are used, by randomizing order for participants

Instrumentation threat

change in the measurement instrument, observer, or measurement procedure during a study that can influence the DV independently of the IV.

Independent-samples t-test

used to determine whether the means of two independent groups differ statistically.