Comparison of an experimental mean with a known value

Comparison of an experimental mean with a known value 

In order to decide whether the difference between x and is significant, that is to test Hq population mean = p, the statistic t is calculated  

If t (i.e. the calculated value of t without regard to sign) exceeds a certain critical value then the null hypothesis is rejected. The critical value of t for a particular significance level can be found from Table A.2. For example, for a sample size of 10 (i.e. 9 degrees of freedom) and a significance level of 0.01, the critical value is tg = 3.25, where, as in Chapter 2, the subscript is used to denote the number of degrees of freedom. 

In a new method for determining selenourea in water, the following values were obtained for tap water samples spiked with 50 ng ml of selenourea  

The mean of these values is 50.06 and the standard deviation is 0.956. Adopting the null hypothesis that there is no systematic error, i.e. p = 50, and using equation (3.1) gives 

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