Chapter 20, Problem 56E

Crawling Researchers at the University of Denver Infant Study Center wondered whether temperature might influence the age at which babies learn to crawl. Perhaps the extra clothing that babies wear in cold weather would restrict movement and delay the age at which they started crawling. Data were collected on 208 boys and 206 girls. Parents reported the month of the baby’s birth and the age (in weeks) at which their child first crawled. The table gives the average Temperature (°F) when the babies were 6 months old and average Crawling Age (in weeks) for each month of the year. Make the plots and compute the analyses necessary to answer the following questions. (Janette B. Benson, “Season of birth and onset of locomotion: Theoretical and methodological implications, “Infant Behavior and Development 16(1): 69–81, 1993.)

1. a) Would this association appear to be weaker, stronger, or the same if data had been plotted for individual babies instead of using monthly averages? Explain.
2. b) Is there evidence of an association between Temperature and Crawling Age? Test an appropriate hypothesis and state your conclusion. Don’t forget to check the assumptions.
3. c) Create and interpret a 95% confidence interval for the slope of the true relationship.