Research has shown that for mammals giving birth to a son versus a daughter places a greater strain on mothers. Does this affect the health of their next child? A study compared the birth weights of humans born after a male versus after a female. Summary statistics for the sample of size 76 are given in the following table: the data were normally distributed. Consider a t test, with a directional alternative, to investigate the research hypothesis that birthweight is lower when the elder sibling is male.

(a) Write the null hypothesis and the alternative hypothesis in symbols.
(b) Here is computer output for the / test. Explain what the P-value means in the context of this study.
t = - 2.145, df = 69.54, p-value = 0.0177
alternative hypothesis: true difference in means is less than 0
(c) If α = 0.05, what is your conclusion regarding H0?

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Sex of elder Birthweight (kg) sibling n 33 SD 0.62 Mean Male 3.32 Female 433.63 0.53