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# Mayr et al.(1994) took an SRS of 242 children who visited their pediatric outpatient clinic.

Mayr et al.(1994) took an SRS of 242 children who visited their pediatric outpatient clinic. They found the following frequency distribution for the age (in months) of free (unassisted) walking among the children:

Age (months) ;
9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20
Number of Children ;
13, 35, 44, 69, 36, 24, 7, 3, 2, 5, 1, 1

1. Find the mean, SE, and a 95% CI for the average age for onset of free walking.
2. Suppose the researchers wanted to do another study in a different region, and wanted a 95 % CI for the mean age of onset of walking to have margin of error 0.5. Using the estimated standard deviation for these data, what sample size would they need to take?
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13
35
20
44 21.85073
69
36
24
7
3
2
5
1
1
a
the CI will be 20±t*12^.5/Sdev
20 +- (2.201*3.464)/21.85
19.65
20.34 is the CI
b.
now we habe margin of error = 2.201*?/21.85 = .5
so ? = 24.045925
and...

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