Ok, I am totally confused, this is probably a pure math rather than a statistic question but please enlighten me.
I found the logrank statistic formula being reported in the literature in 2 ways, but I am not sure which one is correct. When I plug the same number in both formula, i get different results for the chi-square.
Which one should I use?
$O$ = total of observed events
$E$ = total of expected events
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$$\frac{(O-E)^2}{E} $$
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$$\frac{O-E}{\sqrt{E}}$$
Which one should be used? The main reason I am asking is because when I apply the weights (W) as in the formula below, it looks like the weights are being cancelled out:
Best Answer
Just read this paragraph from the same page of your book and remember that square of a standard normal distribution is a chi-square distribution. Therefore the two tests are equivalent. You can use any of them.