6. The mean (standard deviation) of In [calcium intake (ng)] among 25 females, 1

Question

6. The mean (standard deviation) of In [calcium intake (ng)] among 25 females, 12 to 14 years of age, below the poverty level is 6.56 (0.64). Similarly, the mean (standard deviation) of In [calcium intake (mg)1 among 40 females, 12 to 14 years of age, above the poverty level is 6.80 (0.76) (20pts). a. What is the appropriate procedure to test for a significant difference in means between the two b. Conduct the test using the 5 step hypothesis method. (In your conclusion, do not simply state that c. Compute a 95% confidence interval for the difference in means between the two groups. Based on groups (2 pts) the null hypothesis was accepted or rejected) (7 pts) the confidence interval, would you make the same conclusion as in 6b? Why or Why not. (2 pts) an equal number of 12- to 14-year-old gitls below and above the poverty level are recruited to study differences in calcium intake. How many girls should be recruited to have an 80% chance of detecting a significant difference (power) using a two-sided test with 057(7 d. Suppose pts) what do you expect to happen to the sample size if we increased our power from 80% to 90% (2 pts)?

Explanation / Answer

a) Two -sample t-test can be used

b)

Two-Sample T-Test and CI

Sample   N   Mean StDev SE Mean
1           25    6.560   0.640    0.13
2           40    6.800    0.760     0.12

Difference = (1) - (2)
Estimate for difference: -0.240
95% CI for difference: (-0.605, 0.125)
T-Test of difference = 0 (vs ): T-Value = -1.31 P-Value = 0.194 DF = 63
Both use Pooled StDev = 0.7167

c)

95% CI for difference: (-0.605, 0.125)

d)

n = 135 , for 80 % power

e)

n = 180 for 90% power

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