Practice t-test designs - analysis:

For each of the following, identify the type of test to be used (the z-test or one of the three t-tests) & explain why that test, comment

on each of the parametric assumptions, comment on each of the seven power factors, and make an overall summary statement regarding power.

Sample size –

            larger sample = higher power, lower sample = lower power.                 

Effect size –

            larger effect = higher power, smaller effect = lower power

Sensitivity of the DV to changes in the IV –

            more sensitive DV’s are more powerful

Alpha – Larger α = higher power, smaller α = lower power

Design – Repeated measures versus independent groups

Directional versus non-directional hypothesis (a.k.a., One-tailed versus two-tailed test) – directional is more powerful

Type of test – parametric versus nonparametric

Good research procedures & materials –

            excellent methods reduce unwanted variability (i.e., “error”)

The director of training in an institution wants to reduce the amount of time schizophrenics spend in the institution.  She proposed

 a new training program that would enroll 28 schizophrenic patients.  She knows that the mean duration of the population

 of schizophrenics’ stay has been 85 weeks but she doesn’t know the standard deviation.

A savvy psychology student thought about the schizophrenic project described above, and decided that the risk of confounding variables

 affecting the proposed project’s outcome was high, so she suggested to the director that a control group of schizophrenics who continue

 to receive the standard training program also be included in the study.  That way, she argued, the treatment group could be compared

 to the control group, thus controlling for confounding variables.

A Physical Education instructor believes that regular exercise can improve students’ academic performance in their other classes. 

She enrolled 45 students into her research project, and hopes to be able to show that students who exercise regularly over two

semesters will have a mean GPA that is considerably higher than it was prior to the start of the exercise program.

A researcher interested in memory wanted to study recall based on pictures versus words.  She tested eight students who saw slides of nouns

 printed on them, and another eight students who saw pictures of the things named by the nouns.  After viewing the slides, students were given

 a recall test and the number of correctly remembered items was measured.

A savvy psychology student thought about the memory study, and suggested that eight participants per group are far too few for an adequate

statistical test.  She suggested that the n’s per group be increased to 32, but with the rest of the proposed study still the same.