At what age do babies learn to crawl? Does it depend on the time of the year that babies were born?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 four feet within one minute. The resulting data were grouped by month of birth: January, May, and September.

	Average
Birth Month	Crawling Age	SD	n
January	29.84	7.08	32
May	28.58	8.07	27
September	33.83	6.93	38

Crawling age is given in weeks. Assume the data are three independent SRSs, one form each of the three populations (babies born in a particular month) and that the populations of crawling ages have normal distributions. A partial ANOVA table is given below.

Analysis of Variance for crawling age.

Source	df	Sums of Squares	Mean Square	F-ratio
Birth Month		505.26
Error			53.45

Total

Easy Multiple Choice Questions:

1. The numerator degrees of freedom for the ANOVA F test are

a. 2

b. 3

c. 94

d. 96

2. The denominator degrees of freedom for the ANOVA F test are

a. 2

b. 3

c. 94

d. 96

The alternative hypothesis for the ANOVA F test is

a. the mean age at which babies learn to crawl is highest in September

b. the mean age at which babies learn to crawl is different for the three birth months

c. the mean age at which babies learn to crawl is the same for January and May

d. None of the above

4. The pooled standard deviation is

a. 7.31

b. 17.63

c. 22.48

d. 26.73

5. The value of the ANOVA F-statistic is

a. 3.15

b. 4.73

c. 6.30

d. 9.45