1. At what age do babies learn to crawl? Does it take longer to learn in the winter when babies are often bundled in clothes that restrict their movement? Data were collected at the University of Denver Infant Study Center where parents and their babies participated in one of a number of experiments between 1988 and 1991. Parents reported the age (in weeks) at which their child was first able to creep or crawl a distance of four feet within one minute. The researchers also recorded the average outdoor temperature (in °F) six months after each baby's birthdate. For each month of the year, the researchers selected one baby, at random, born in that month. The least-squares regression line for the 12 data points (one for each month) was computed. Here is a scatterplot of average crawling age versus average outdoor temperature six months after birth followed by a plot of the residuals versus average outdoor temperature six months after birth.
Which of the following statements is supported by these plots?
A. There is no striking evidence in these plots that the assumptions for regression are violated.
B. There is an outlier in the plots suggesting that our above results must be interpreted with caution.
C. There is an influential observation in the plot, which should be deleted.
2. Has the number of home runs hit by major league teams been increasing over time? For the 41 years from 1960 to 2000, the average number of home runs hit per game per team was computed. A simple linear regression was used to study the trend in the average number of home runs over the period 1960 to 2000, by using year to predict average number of home runs. The following results were obtained.
We use these results to test the hypotheses
where ρ is the correlation between year and the average number of home runs hit per game per team. The P-value of this test is
A. between 0.005 and 0.0025.
B. between 0.0025 and 0.001.
C. 0.0005.