At what age do babies learn to crawl? does it take longer to learn in the winter when babies are bundled in clothes to restrict their movement? data was collected from parents who brought their babies to new york university infant study center to participate in one of a number of experiments between 1988 and 1991. parents reported ages (in weeks) at which their child was first able to crawl a distance of four feet within one minute. the researchers also recorded the average outdoor temperature (in f) 6 months after the babies; date of birth. the resulting data were grouped by month of birth and all data for babies born on a given month averaged together. if you fit the least-squares line to the 12 data points (one for each month) you obtain the following results from a software package. notice that the temperature given is taken as the explanatory variable and crawling age as the response variable. the dependent variable is the average crawling age.

r squared = 49.0%
s = 1.319 with 12 ? 2 = 10 degrees of freedom

variable variable coefficient s. e. of coefficient

constant 35.6781 1.318

temp. –0.077739 0.0251

a. (–0.134, –0.022)
b. (0.055, 0.105)
c. (0.024, 0.136)
d. (–0.103, –0.053)
e. (0.053, 0.103)