4.16 Identify hypotheses, Part II. Write the null and alternative hypotheses in words and
using symbols for each of the following situations.
(a) Since 2008, chain restaurants in California have been required to display calorie counts of
each menu item. Prior to menus displaying calorie counts, the average calorie intake of diners
at a restaurant was 1100 calories. After calorie counts started to be displayed on menus, a nutritionist collected data on the number of calories consumed at this restaurant from a random sample of diners. Do these data provide convincing evidence of a difference in the average calorie intake of a diners at this restaurant?
(b) Based on the performance of those who took the GRE exam between July 1, 2004 and June 30, 2007, the average Verbal Reasoning score was calculated to be 462. In 2011 the average verbal score was slightly higher. Do these data provide convincing evidence that the average GRE Verbal Reasoning score has changed since 2004?
4.18 Age at first marriage, Part II. Exercise 4.14 presents the results of a 2006 – 2010 survey showing that the average age of women at first marriage is 23.44. Suppose a researcher believes
that this value has increased in 2012, but he would also be interested if he found a decrease. Below
is how he set up his hypotheses. Indicate any errors you see.
4.20 Thanksgiving spending, Part II. Exercise 4.12 provides a 95% confidence interval for the
average spending by American adults during the six-day period after Thanksgiving 2009: ($80.31,
(a) A local news anchor claims that the average spending during this period in 2009 was $100.
What do you think of this claim?
(b) Would the news anchor’s claim be considered reasonable based on a 90% confidence interval?
Why or why not?
4.22 Gifted children, Part I. Researchers investigating characteristics of gifted children col-
lected data from schools in a large city on a random sample of thirty-six children who were identified as gifted children soon after they reached the age of four. The following histogram shows the distribution of the ages (in months) at which these children first counted to 10 successfully. Also provided are some sample statistics.
(a) Are conditions for inference satisfied?
(b) Suppose you read on a parenting website that children first count to 10 successfully when they
are 32 months old, on average. Perform a hypothesis test to evaluate if these data provide
convincing evidence that the average age at which gifted children first count to 10 successfully
is different than the general average of 32 months. Use a significance level of 0.10.
(c) Interpret the p-value in context of the hypothesis test and the data.
(d) Calculate a 90% confidence interval for the average age at which gifted children first count to
10 successfully. (e) Do your results from the hypothesis test and the confidence interval agree? Explain.
4.24 Gifted children, Part II. Exercise 4.22 describes a study on gifted children. In this study, along with variables on the children, the researchers also collected data on the mother’s and father’s IQ of the 36 randomly sampled gifted children. The histogram below shows the distribution of mother’s IQ. Also provided are some sample statistics.
(a) Perform a hypothesis test to evaluate if these data provide convincing evidence that the average IQ of mothers of gifted children is different than the average IQ for the population at large, which is 100. Use a significance level of 0.10.
(b) Calculate a 90% confidence interval for the average IQ of mothers of gifted children.
(c) Do your results from the hypothesis test and the confidence interval agree? Explain.