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Suggested answer to exercise: Analyses for qualitative data, 5

Question 5: What is a trend test and how would you interpret the one presented here?

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Suggested answer

The trend test is the Armitage chi-squared test for trend or the Mantel-Haenszel test
for trend.
It works by assigning numerical values to each category and then estimating
the best prediction of one variable by the other as a simple

*y* = constant1 + constant2 × *x*.

The chi-squared test for trend tests the null hypothesis that there
is no such prediction and constant2 = 0.
The calculated chi-squared value is 20.6 with 1 degree of freedom with
an associated P-value smaller than 0.001.
This provides strong evidence for a trend in the proportions and so
we would conclude that the proportion of males who are seropositive increases with age.

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Last updated: 27 July, 2009.

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