# 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

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 from parents who brought their babies into the University of Denver Infant Study Center to participate in one of a number of experiments between 1988 and 1991. Parents reported the birth month and the age at which their child was first able to creep or crawl a distance of 4 feet within 1 minute. The resulting data were grouped by month of birth: January, May, and September:

$$\begin{array}{c} & Crawling\ age \\ \hline Birth\ month & Mean & St.dev. & n \\ \hline January & 29.84 & 7.08 & 32 \\ May & 28.58 & 8.07 & 27 \\ September & 33.83 & 6.93 & 38\end{array}$$

Crawling age is given in weeks. Assume the data represent three independent simple random samples, one from each of the three populations consisting of babies born in that particular month, and that the populations of crawling ages have Normal distributions. A partial ANOVA table is given below

. $$\begin{array}{c}Source & Sum\ of\ squares & DF & Mean\ square\ F \\ \hline Groups & 505.26\\ Error & & &53.45\\ Total\end{array}$$

What are the degrees of freedom for the groups term?

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pattererX
Given: Groups represent the birth month. k represent the groups. k=3 The degrees of freedom for the groups term is obtained as below: $$\displaystyle{d}{f}_{{{g}{r}{o}{u}{p}{s}}}={k}-{1}$$
$$\displaystyle={3}-{1}$$
$$\displaystyle={2}$$ Thus, the degrees of freedom for the groups term is 2.