1. Age at onset of dementia was determined for a sample of adults between the ages of 60 and 75. For 15 subjects, M = 67.2 and s = 3.06. Use this information to answer the following:
a. Based on the data you have and the normal curve tables, what percentage of people might start to show signs of dementia at or before age 62?
b. If you consider the normal range of onset in this population to be +/-1 z-score from the mean, what two ages correspond to this?
c. A neuropsychologist is interested only in studying the most deviant portion of this population: those individuals who fall within the top 10% and the bottom 10% of the distribution. She must determine the ages that mark these boundaries. What are these ages?
2. (Non-SPSS) For each of the following scenarios, compute the effect size and state (whether it is approximately small, medium, or large).
a. Participants in an inpatient study of treatment for OCD complete an anxious feelings inventory which is then compared to the general population. The sample mean is M = 27.2. The mean in the general population of inpatients on this inventory is M = 35.5, and the population standard deviation is 1.9.
b. A mood assessment in a sample of 15 gym members has a mean of 87 and a standard deviation of 6. The mean in the general population on this measure is 79.