psyc ch 8-11

what is the effect on the value of the test statistic for a 2 independent sample test if the pooled sample variance is doubled

decrease

does increasing degrees of freedom make it easier or harder to reject the null hypothesis

easier

S(m)

estimated standard error

S(M1-M2)

estimated standard error for the difference

S(MD)

estimated standard error for the differences scores

selecting related samples increases standard error and reduces power (t/f)

false (standard error is decreased and power goes up)

A researcher computes a two-independent sample t test and finds that the result is undefined (the denominator is equal to 0). This happens when there is no difference between the two groups (i.e., the mean difference is equal to 0).

false (the only way the denominator would equal 0 would be if there were no variability in either sample)

does changing from a one-tailed test to a two-tailed test make it easier or harder to reject the null hypothesis

harder

does decreasing the alpha level make it easier or harder to reject the null hypothesis

harder

does using the standard deviation of a sample rather than the standard deviation of the population make it easier or harder to reject the null hypothesis

harder (more difficult to make a statistical decision w/ less info)

what is the effect on the value of the test statistic for a 2 independent sample test when the total sample increases

increase

advantages of related samples

more practical, reduces standard error, increases power

what is the effect on the confidence interval if the sample size increases

narrow

what is the effect on the value of the test statistic for a 2 independent sample test when the level of significance decreases

no effect

what is the effect on the confidence interval if the sample mean increases

none

what is the effect on the confidence interval if the standard deviation of the population increases

none

S(P)

pooled sample standard deviation

types of related-samples t test

pre post, within subjects, matched pairs

A researcher counted the number of aggressive encounters among children who were playing with worn and broken toys. Next the children watched other children playing with new, shiny toys. Finally, the first group of children resumed playing with the worn and broken toys, and the researchers again counted the number of aggressive encounters.

related

An investigator gathered many case histories of situations in which identical twins were raised apart—one in a "good" environment and one in a "bad" environment. The group raised in the "good" environment was compared that raised in the "bad" environment on attitude toward education.

related

One group was deprived of REM (rapid eye movement) sleep and the other was not. At the sleep lab, participants were paired and randomly assigned to one of two conditions. When those in the deprivation group began to show REM, they were awakened, thus depriving them of REM sleep. The other member of the pair was then awakened for an equal length of time during non-REM sleep. The next day all participants filled out a mood questionnaire.

related

Patients with seasonal affective disorder (a type of depression) spent 2 hours a day under bright artificial light. Before treatment the mean depression score was 20.00, and at the end of one week of treatment the mean depression score was 6.4.

related

s or SD

standard deviation

S(D)

standard deviation of the difference scores

to compute the related samples t test, we assume independence within groups, but not between groups (t/f)

true

One group was deprived of REM sleep and the other was not. At the sleep lab, participants were randomly assigned to one of two groups. When those in the deprivation group began to show REM, they were awakened, thus depriving them of REM sleep. The other participants were awakened during non-REM sleep. The next day all participants filled out a mood questionnaire.

two-independent

Thirty-two first-year students applied for a sophomore honors course. Only 16 could be accepted, so the instructor flipped a coin for each applicant with the result that 16 were selected. At graduation, the instructor compared the mean GPA of those who had taken the course to the GPA of those who had not to see if the sophomore honors course had an effect on GPA.

two-independent

what is the effect on the confidence interval if the level of confidence is increased (from 95% to 99%)

widen

what is the effect on the confidence interval if the standard deviation of the sample increases

widen