Suggested answers to exercise: Outcome of the MRC streptomycin trial, 4

Question 4: Report both tests to an appropriate number of decimal places.

Suggested answer

The linear association test gives chi-squared = 17.761 with P = .000. We need give only two decimal places for the chi-squared test statistic, so 17.761 becomes 17.76. We should write .000 as P < 0.001. We do this because the probability can never be exactly zero. Also, we should put a zero before the decimal point for numbers between nought and one. This makes them easier to read.

We could say that the test of linear association for radiological assessment was highly significant, chi-squared = 17.76, d.f. = 1, P < 0.001. The difference in survival was also highly significant, chi-squared = 7.38, d.f. = 1, P = 0.007.

Note that 7.376 becomes 7.38 to two decimal places, because the last digit, 6, goes up.

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Last updated: 15 November, 2006.

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