Females of many animals can recognize their own offspring by voice. But how long does this vocal memory last? Briefer et al. (2012) tested the responses of mother goats to their offspring 11 to 17 months after the kids were independent of their mothers.

They scored the behavioral response of each of nine mothers (based on how fast her response was, how often the offspring called in return, and how long the mother looked at the loudspeaker) when played a recording of one of her former kids. The researchers also scored her behavioral response to recordings of unrelated kids of the same age. The scores are below.

a. Calculate a 95% confidence interval for the mean difference in response score for former kids compared to unrelated kids.

b. Test the null hypothesis that there is no difference between the response scores of mothers to former kids compared to unrelated kids.

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Mother goat 11 22 33 44 55 66 77 88 99 Response score to former kid -3.23-3.23 -1.78-1.78 -0.72-0.72 -0.57-0.57 0.320.32 0.460.46 1.071.07 1.771.77 2.222.22 Response score to unrelated kid -3.26-3.26 -2.71-2.71 -0.13-0.13 -3.24-3.24 -2.56-2.56 -0.62-0.62 0.120.12 1.121.12 1.741.74