Final answer:
The AAP recommends breastfeeding for 1 year or longer, but the hypothesis test is to determine if the U.S. mean weaning age is less than four years. The sample data has a mean of nine months, suggesting that American weaning age is statistically less than the global average. A one-sample t-test would be used to test this hypothesis.
Step-by-step explanation:
The American Academy of Pediatrics (AAP) does not specify an upper age limit for breastfeeding, but they recommend exclusive breastfeeding for about the first six months of a baby's life, followed by continued breastfeeding as complementary foods are introduced, with continuation of breastfeeding for 1 year or longer as mutually desired by mother and infant. In contrast, the scenario given for the hypothesis test involves determining if the mean weaning age in the United States is less than four years old. Since the global average weaning age is around four to five years according to La Leche League International, but the U.S. mothers reported a mean weaning age of nine months, the hypothesis test is set to demonstrate that the U.S. mean is statistically less than the global average.
The hypothesis being tested (null hypothesis) is that the average weaning age in the U.S. is equal to or more than four years, and the alternative hypothesis is that it is less. With a sample mean of nine months and a standard deviation of four months, we should be conducting a one-sample t-test to determine if there is enough evidence to reject the null hypothesis in favor of the alternative hypothesis. If the p-value obtained from the test is less than a chosen significance level (commonly 0.05), we would reject the null hypothesis and conclude that the mean weaning age in America is indeed less than four years.