Re: Chi Square

Natalie Vivien wrote:
"A large hospital schedules discharge support staff assuming that
patients leave the hospital at a fairly constant rate throughout the
week. However, because of increasing complaints of staff shortages, the
hospital administration wants to determine whether the number of
discharges varies by the day of the week. Use Chi-Square Test to test
the assumption that patients leave the hospital at a constant rate."

Day Discharges Admittance
Sun 44 68
Mon 78 87
Tue 90 90
Wed 94 84
Thu 89 82
Fri 110 84
Sat 84 71

1) I thought Chi Square is used to test the Ho: The data follows a type
of non-normal distribution. What is it actually used for?

That is one appliaction of the chi-square goodness-of-fit test.

2) To be more specific, what does a computed Chi square statistic mean?
I know a t-statistic is computed to show whether the mean difference of
two populations is the same or not. So what does a Chi Square statistic
mean?

It depends on context. there are many different chi-squared tests and
all have in common only that they produce statistics that can be
approximated by a chi-square distribution.

In some cases one could consider the chi-square test a test of an
association, a difference in proportions, a test of independence, a
test of whether an odds ratio differs from 1 and so forth.

3) How do you detect a Chi Square is needed? I couldn't tell that a Chi
Square is required to test the assumption that patients leave the
hospital at a constant rate.

In this case the chi-square test of independence might be appropriate
to test whether the discahrge rates are indepedent of the day of he
week.

Thom

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