Independent-Samples t-test

1. When people learn a new task, their performance usually improves when they are tested the next day,

but only if they get at least 6 hours of sleep. The following data demonstrate this phenomenon. The

participants learned a visual discrimination task on one day, and then were tested on the task the

following day. Half of the participants were instructed to have at least 6 hours of sleep and the other

half were kept awake all night. Higher scores indicate better performance on the visual discrimination

task. Is there a significant difference between the two conditions? Use a two tailed test with

=.01. Be sure to state tcrit and tobt. Provide a one to two sentence summary of the findings and include a statistical sentence.

No Sleep 6 Hours of Sleep

5 6

1 10

2 14

3 12

4 18

Statistical hypotheses:

Tcrit:

Pooled variance:

Estimated standard error:

Tobt:

Decision:

2.A biopsychologist studies the role of the brain chemical serotonin in aggression. One sample of rats

serves as a control group and receives a placebo. A second sample of rats receive a drug that lowers

brain levels of serotonin. Then the researcher tests the animals by recording the number of aggressive

responses each of the rats display. The data are presented below. Use

=.05, two-tails to determine if the drug had a significant effect on aggression. Be sure to state tcrit and tobt. Provide a one to two sentence summary of the findings and include a statistical sentence.

Low Serotonin Control

n=6 n=8

M=22 M=14

SS=108 SS=180

Statistical hypotheses:

Tcrit:

Pooled variance:

Estimated standard error:

Tobt:

Decision: