For Questions 7- 15 At what age do babies learn to crawl? Does it take longer to

Question

For Questions 7- 15 At what age do babies learn to crawl? Does it take longer to learn in the winter when babies are often bundlecd in clothes that restrict their movement? Data were collected at the University of Denver Infant Study Center where parents and their babies participated in one of a number of experiments between 1988 and 1991. Parents reported the age (in weeks) at which their child was first able to creep or crawl a distance of four feet within one minute. The researchers also recorded the average outdoor temperature (in F) six months after each baby's birthdate. For each month of the year, the researchers selected one baby, at random, born in that month. If we fit the least-squares line to the 12 data points (one for each month) we obtain the following results from a software package. Notice that temperature is taken as the explanatory variable and crawling age as the response. s 1.319 Variable Intercept Temperature Parameter estimate 35.6781 0.077739 Standard error of estimate 1.318 0.0251 Here is a scatterplot of average crawling age versus average outdoor temperature six months after birth followed by a plot of the residuals versus average outdoor temperature six months after birth.

Explanation / Answer

7) Temperature (this is the independnet variable, hence explanatory) (d)

8) From scatter plot, it seems there is strong negative correlation among average crawling age and temperature. (d)

10) t=-0.077739/0.0251=-3.10 (b)

12) t critical at df=n-2, alpha=0.10 is 1.8124

90% c.i=-0.078+-1.8124*0.0251

= -0.078+-0.045 (b)

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