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. If we fit the least-squares line to the 12 data points (one for each month) we obtain the following results from a software package. Notice that temperature is taken as the explanatory variable and crawling age as the response.
s = 1.319
The quantity s = 1.319 is an estimate of the standard deviation of the deviations in the simple linear regression model. The degrees of freedom for s2 are
A. 1.74.
B. 10.
C. 11.
6. 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.
Based on the equation of the least-squares line, we use software to predict the average number of home runs hit per game per team for the year 2001. We obtain the following.
A 95% prediction interval for the average number of home runs hit per game per team for the year 2001 is
A. 1.9134 ± 0.545.
B. (1.7481, 2.0786).
C. 1.9134 ± 0.0817.