Question

what is the primary difference between a within subjects and a between subjects design? give an example of a test used for between subjects design

Answer 1

what is the primary difference between a within subjects and a between subjects design? give an example of a test used for between subjects design

Between-subjects (or between-groups) study design: different people test each condition, so that each person is only exposed to a single treatment or exposure. Here different groups of subjects are compared.

Within-subjects (or repeated-measures) study design: the same person tests all the conditions (i.e., all the different treatment or exposures). Here same group of subjects compared over time or different conditions.

Example : Between-subjects design:

ANOVA test used.

Problem:

Air traffic controllers perform the vital function of regulating the traffic of passenger planes. Frequently, air traffic controllers work long hours with little sleep. Researchers wanted to test their ability to make basic decisions as they become increasingly sleep deprived. To test their abilities, a sample of 6 air traffic controllers is selected and given a decision-making skills test following 12-hour, 24-hour, and 48-hour sleep deprivation. Higher scores indicate better decision-making skills. Data as follows
12 Hours 24 Hours 48 Hours
22 17 15
17 20 20
32 22 21
25 20 12
21 13 14
19 20 13

Result:

Three different groups are compared.

group	N	Mean
12 hours	6	22.6667
24 hours	6	18.6667
48 hours	6	15.8333

Null hypothesis: µ1= µ2= µ3

Alternative hypothesis: At least two of the population means differ from one another.

Analysis of Variance

Source	DF	SS	MS	F-Value	P-Value
group	2	141.4	70.72	4.03	0.040
Error	15	263.5	17.57
Total	17	404.9

Calculated F=4.03, P=0.040 which is < 0.05 level of significance. Ho is rejected.

We conclude that decision making skills are different for the three groups.