Matched-Subjects (and Within-Subjects) Experiment

Question 1

to improve the chances of detecting an effect in spite of large within-group variation (increase power) you can use……..

Answer 1

matched random assignment

Question 2

matched random assignment:

Answer 2

find participants who are similar on some variable highly relevant to the DV then randomly assign subjects of each pair to the two groups (i.e. the two levels of the IV)

Question 3

To compare matched pairs on the DV for consistent differences within pairs on DV what test would you use?

Answer 3

Paired T-test

Question 4

Why would you use a paired t-test and not an independent t-test?

Answer 4

A paired t-test controls for differences between the pairs (i.e. within each group) therefore greater chance that the effect is not due to chance

Question 5

when would you use an ANOVA instead of a paired t-test when using matched random assignment?

Answer 5

when their are more than two groups (more than two levels of the IV)

Question 6

An example of “pairing” participants if examining the impact of Educational TV on GPA would be

Answer 6

• previous GPA
• academic aptitude
• academic motivation

Question 7

By not pairing you risk:

Answer 7

the within group variance to be larger than the between group variance (effect)

Question 8

True or False: when pairing/matching participants you must use a variable that is related to the DV?

Answer 8

True

Question 9

if you do not use a variable related to the DV while matching pairs, what happens?

Answer 9

you fail to remove within group variance in the DV, therefore you lose statistical power
you only have half as many df because it depends on the number of pairs

Question 10

Note: when using an ANOVA you would identify sets of _____ or more participants who are similar in DV (or related variable)

Answer 10

when using an ANOVA you would identify sets of 3 or more participants who are similar in DV (or related variable)
- by doing this you error variance decreases, and F ratio and power increases

Question 11

Drawbacks of within subject design:

Answer 11

practice effects
fatigue effects
carry-over effects
sensitization
maturation
history

Question 12

when using a matched groups OR a within-subjects design with one IV, your ANOVA test will involve tests of:

Answer 12

• main effect due to the IV
• main effect due to the matched groups (blocks) or subjects (if its within)

Question 13

True or False: you can use matched groups or within-subject designs with 2 IVS?

Answer 13

True