Crawl before you walk At what age do babies learn to crawl? Does it take longer to learn in the winter, when babies are oft en bundled in clothes that restrict their movement? Perhaps there might even be an association between babies’ crawling age and the average temperature during the month they fi rst try to crawl (around six months aft er birth). Data were collected from parents who brought their babies into the University of Denver Infant Study Center to participate in one of a number of experiments. Parents reported the birth month and the age at which their child was fi rst able to creep or crawl a distance of four feet within one minute. Information was obtained on 414 infants, 208 boys and 206 girls. Crawling age is given in weeks, and the average temperature (in 8F) is for the month that is six months aft er the birth month.

(a) Make a scatterplot that displays the relationship between average crawling age and average temperature. Be sure to think about which is the explanatory variable.

(b) Describe the direction, form, and strength of the relationship. What do you conclude about when babies learn to crawl?

Average temp. (F) 6 mo after birth Birth month Average crawling age (wk) January February March April May June 29.84 66 30.52 73 29.70 72 31.84 63 28.58 52 31.44 39 July 33.64 33 August 32.82 30 September 33.83 33 October 33.35 37 November 33.38 48 December 32.32 57