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# Confidence Interval for Mean Difference

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A developmental psychologist would like to determine how much fine motor skill improves for children from age 3 to age 4. A random sample of n = 15 3 year old children and a second sample of n = 15 4 year olds are obtained. Each child is given a manual dexterity test that measure fine motor skills. The average score for the older children was M = 40.6 with SS = 430 and the average for the younger children was M = 35.4 with SS = 410. Using these data,

a. Make a point estimate of the population mean difference in fine motor skills.
b. Make an interval estimate so you are 95% confident that the real mean difference is in your interval.
c. Make an interval estimate so you are 99% confident that the real mean difference is in your interval.
d. Based on your answers from b and c, do these data indicate a significant change using a two-tailed