At what age do babies learn to crawl? Does it depend on the time of year that babies were born? Data were collected from parents who brought their babies into the University of Denver's 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. Crawling age is given in weeks. Assume that the data can be considered as three independent random samples (one from each of the populations composed of babies born in that particular month) and that the populations of crawling ages have Normal distributions. An ANOVA F test was run on the data. The following shows a portion of the results. 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 answer options is correct.

Question

At what age do babies learn to crawl? Does it depend on the time of year that babies were born? Data were collected from parents who brought their babies into the University of Denver's 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. Crawling age is given in weeks. Assume that the data can be considered as three independent random samples (one from each of the populations composed of babies born in that particular month) and that the populations of crawling ages have Normal distributions.  An ANOVA F test was run on the data. The following shows a portion of the results.  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 answer options is correct.

Quizplus · Accepted Answer

The ANOVA F test is used to determine if there is a significant difference in means among three or more groups. In this case, the three groups are the babies born in January, May, and September. The null hypothesis is that the mean crawling ages for all three groups are equal, and the alternative hypothesis is that at least one of the means is different. Therefore, choice B is the correct answer.

At What Age Do Babies Learn to Crawl? Does It