CASE II

In an effort to test the hypothesis that the drug chlorpromazine enhances the performance of schizophrenics, two clinical investigators (Drs. F. and D.) randomly selected 30 schizophrenics from two hospitals in Northeastern United States.The schizophrenics were asked to perform an 'editing' task - crossing out all e's and f's. All participants were asked to perform the task twice.

Before performing the task for the first time, they were injected with chlorpromazine by Dr. F.Before performing the task for the second time, they were injected with a saline solution (a placebo) by Dr. D.Each time, the investigators counted the number of errors made by each participant, and also collected data on a self-report measure of anxiety.

Results indicated that significantly more errors were made in the saline condition than in the chlorpromazine condition; also the participants reported significantly more anxiety in the saline condition than in the chlorpromazine condition.Dr. F. and Dr. D. concluded that, as hypothesized, chlorpromazine facilitates cognitive functioning and minimizes anxiety in this type of patient.

a) Research Design:Please describe the research design and explain your choice.

In doing so, label the study as:

• e.g., experimental, correlational, quasiexperimental, ex-post facto, time series etc;

between participants or within participants, or mixed design;

lab or field.

b) Independent variable(s):Please indicate whether there are independent variable(s) and if so, what they are.In describing any independent variable(s),

• please name the specific variable(s)

indicate the levels (i.e., conditions) of each variable and

also describe each variable as manipulated or non-manipulated.

c) Dependent variable(s): Please indicate whether there are dependent variable(s) or any measures. In describing the dependent variable(s)/measures,

• please name the specific variable(s),

label each variable as nominal, ordinal, interval or ratio, and

also explain why you gave the answer(s) you provided in part b.

d) Internal Validity:Please explain any sources of threat to internal validity; alsoplease explain any features in favor of internal validity.(Use 'technical' terms where relevant, e.g., confounding, demand characteristics, regression to the mean, mortality threat, etc., and explain how the terms relate to the situation).

e) External Validity:Please explain any sources of threat to external validity; alsoplease explain any features in favor of external validity.(Use 'technical' terms where relevant.)

f) Statistical Analysis:Please suggest descriptive statistics that are appropriate for the data, andan inferential statistic or statistics that can test the hypothesis.Where appropriate, also indicate whether the analyses are parametric or non-parametric and why those analyses (or that analysis) are (is) are the 'right' ones.