A random sample of 14 college female students revealed their average height was 66.1 inches.
a) How many students should be in a samle if a 95% confidence interval is to have a margin of error of only plus/minus 1 inch?
Is that the only information you were given? Were you not told the standard deviation for the 14 that were measured? It seems to me that you need some infomation on the inherent variability of the height distribution. None has been provided.
Here is the complete problem:
A random sample of 14 college female students revealed their average height was 66.1 inches.
a) Explain to someone who knows no statistics why we can't just say that 66.1 inches is the average height of all female students.
b) Te researcher announced a margin or error of plus/minus 1.75 inches for 95% confidence. Write down the 95% confidence interval for the height of all female students. Explain clearly what"95% confidence" means.
c) State the formula for the margin of error of a confidence interval for the mean. Explain what each term in this expression represents. Explain how changing these terms one at a time will affect the size of the confidence interval.
d) How many students should be in a sample if a 95% confidence interval is to have a margin of error of only plus/minus 1 inch?
Can you help me further? Thanks.
The standard error of the mean (SE) = the standard deviation (SD) divided by the square root of n - 1.
SE = SD/sq rt (n-1)
You have the values of SE and n. Substitute those into the formula to get the SD. Then use this SD and SE of 1 to find your new n value.
This should answer your original question. Thanks for asking.
Thank you for the clarification...very appreciated. K
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