Re: confidence interval q.

[Jay Warner]

B. Draw the picture of the sample distribution. A Normal (we presume) 
centered on x-bar. If you were to go back and collect n measurements 
again, from the same source, the area under the curve between any two 
x-axis values indicates the probability that the average of the second 
group would fall in that range. Mark the 95% CI limits. The area under 
the curve between the limits includes 95 of the averages you will get, 
if you resample 100 times - 95%.

Now mark the 90% CI limits. The area between them is only 90%. Thus, 
they must be closer to the center point (the first observed x-bar) than 
the 95% limits, which cover more area.

HTH
Jay
Ben wrote:

Below is a problem that has me stumped.  Would be grateful for an
answer.
A random sample of size n is collected from a population, and from the
data collected a 95% confidence interval for the mean of the
population is computed..  Which of the following changes in condition
would definitely result in a confidence interval with a smaller width
than the one computed.
A – and increased in the population standard deviation
B - a decrease in the confidence level requested from 95% - 90%
C - A decrease in the size of the sample obtained
D - All of the above
E - None of the above
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