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Exhibit 3.31 Histogram of difference in each teen’s page views
is taken in our sample, the interval will be even tighter (< 0.74832
). The larger
the sample, the smaller the interval for a particular confidence interval.
Let us now move to a more sophisticated form of analysis, which answers
questions related to our ability to generalize the sample result to the entire teen
population. In the Data Analysis tool, there is an analysis called a t-Test . A t-test
examines whether the means from two samples are equal or different; that is,
whether they come from population distributions with the same mean or not. Of
special interest for our data is the t-Test: Paired Two Sample for Mean .Itisused
when before and after data is collected from the same sample group, in our case the
same 100 teens being exposed to both the new web-site and the old .
By selecting t-Test: Paired Two Sample for Means from the Data Analysis menu,
the two relevant data ranges can be input, along with a hypothesized mean differ-
ence, 0 in our case, because we will assume no difference. Finally an alpha value is
requested. The value of alpha must be in the range 0 to 1. Alpha is the significance
level related to the probability of making a type 1 error (rejecting a true hypothe-
sis); the more certain you want to be about not making a type 1 error, the smaller the
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