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# Critical value and test statistic

Posted on 2006-11-09

The general population has the mean (5/1000); and the test sample has

(15/5000).

However, we don't know the sd. In this case, how to calculate t value?

If I use the critical-value method with α =0.05, then I come up with

the critical value, -1.645158

My question is how to calculate t value without knowing the sd at all?

The formula is t = (x bar - mu 0) / (sd/sqrt(n)).

so, it could be:

(5/1000 - 15/5000)

--------------------------

sd /sqrt(5000)

thx

ej