STA442/1008 Assignment 10

Quiz in Tutorial on Friday March 30th

1. In a study of the psychology of attention, subjects attempted to solve word problems while listening to distracting backgound noise. The distracting material was either music, or spoken words related to the problem they were trying to solve. The distracting material was presented at three different levels of loudness. Each subject attempted 10 problems at each combination of loudness and type of distraction, for a total of 60 problems. Order of presentation was randomized. Data for each subject are number correct in each of the six treatment combinations, and are avalable in distract.data. Don't forget to look at the data before you start analyzing it.
   1. How many factors are there in this study? Classify each one as between cases or within cases.
   2. Using the multivariate appoach to repeated measures, carry out the appropriate analysis, obtaining F-tests for all main effects and interaction(s). You could follow up the analysis with Bonferroni corrected matched t-tests, but don't bother this time.
   3. Prepare a plot of the means. You can do it by hand, or use Excel or a similar program. Either way, bring your plot to the quiz. You may hand it in.
   4. Your plot suggests that the interaction and one of the main effects (not the other one) should be interpreted. State your conclusions in plain language.
2. Mantids are insects, kind of like crickets or grasshoppers. When frightened, they emit loud noises that function as alarm calls. I believe they make the sounds by rubbing their hind legs together. The frequency (number of calls per minute) may indicate how alarmed the mantids are.

   In this study, caged mantids (either Female or Male) were randomly assigned to be exposed to one of four predators (birds), and the number of alarm calls per minute was recorded. Each mantid was tested at three distances from the predator: 8 cm, 13 cm and 18 cm. The three distances were presented in different randomly chosen orders, but we will ignore order for this assignment.

   The data file mantids.data has three lines of data per insect. The variables are

   • Case identification number: Repeated on each line.
   • Sex: 0=Male, 1=Female. Repeated on each line.
   • Order of presentation: Repeated on each line. Ignore this.
   • Predator (bird): Numbered 1-4. Repeated on each line.
   • Distance: Distance from the predator in centimeters (1=8cm, 2=13cm, 3=18cm).
   • Number of alarm calls per minute

    

   1. How many factors are there in this study? Classify each one as between cases or within cases.
   2. Using the multivariate approach to repeated measures, test all main effects and interactions. Be ready to give the F statistic and p-value for any effect.
   3. Obtain sample means that will let you state what is happening, only for the significant main effects. This is surprisingly challenging. For example, are you really getting the marginal means for sex?

Please bring both sets of log and list files to the quiz. As usual, answers to the questions are not to be handed in. They are just practice for the quiz. Please do not write anything on your printouts except your name and student number. Of course for each job, the log and list files must be from the same run of SAS or marks will be deducted.