Answer: Lactation promotes a temporary loss of bone mass

Chapter 9, Problem 9.40

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Lactation promotes a temporary loss of bone mass to provide adequate amounts of calcium for milk production. The paper Bone Mass Is Recovered from Lactation to Postweaning in Adolescent Mothers with Low Calcium Intakes (Amer. J. Clinical Nutr., 2004: 13221326) gave the following data on total body bone mineral content (TBBMC) (g) for a sample both during lactation (L) and in the postweaning period (P). 9.3 Analysis of Paired Data 351 Infant 1234 Isotopic method 1509 1418 1561 1556 Test-weighing method 1498 1254 1336 1565 Difference 11 164 225 9 Infant 5678 Isotopic method 2169 1760 1098 1198 Test-weighing method 2000 1318 1410 1129 Difference 169 442 312 69 Infant 9 10 11 Isotopic method 1479 1281 1414 Test-weighing method 1342 1124 1468 Difference 137 157 54 Infant 12 13 14 Isotopic method 1954 2174 2058 Test-weighing method 1604 1722 1518 Difference 350 452 540 Subject 1 2 3 4 5 6 7 8 9 10 L 1928 2549 2825 1924 1628 2175 2114 2621 1843 2541 P 2126 2885 2895 1942 1750 2184 2164 2626 2006 2627 a. Does the data suggest that true average total body bone mineral content during postweaning exceeds that during lactation by more than 25 g? State and test the appropriate hypotheses using a significance level of .05. [Note: The appropriate normal probability plot shows some curvature but not enough to cast substantial doubt on a normality assumption.] b. Calculate an upper confidence bound using a 95% con- fidence level for the true average difference between TBBMC during postweaning and during lactation. c. Does the (incorrect) use of the two-sample t test to test the hypotheses suggested in (a) lead to the same conclusion that you obtained there? Explain.