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In which of the following situations would it not be appropriate to use a paired t-test to analyze the data?

A marriage therapist believes that many couples have different perspectives regarding the state of their marriages, prior to the start of couples therapy. In order to determine whether there is difference in marital satisfaction, prior to the start of couples therapy, each member of thirty married couples were individually given a marital satisfaction questionnaire. The mean marital satisfaction scores were then separately calculated for the group of husbands and the group of wives.
A psychologist was interested in determining whether fraternal twins differ in terms the degree to which they are extroverts. A sample of 50 fraternal twins was given the Eysenck personality questionnaire to assess their levels of extraversion.
A psychiatrist believes that a new medication (New Drug) is more effective at reducing the symptoms of depression than a placebo, sugar pill (Placebo). Sixty people with depression were randomly assigned to one of two groups: 1) New Drug or 2) Placebo and were given the assigned drug or sugar pill for 30 days. Each of the 60 participants then completed the Beck Depression Inventory and the mean depression score for the New Drug group is compared to the mean depression score for the Placebo group.
A researcher is interested in determining the effects of sleep deprivation on the accuracy with which mazes are completed. Thirty people are given a test of mazes on Day 1 at 9 am and again on Day 2 at 9 pm after being kept awake for 36 hours. The researcher then compares the number of errors made on Day 1 to Day 2.

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