Statistics

Statistics

SEM = standard error of the mean o

•

= standard deviation of the sample

= sample size

o

• ∗ is the critical value and found in a t-table. On an exam, you would be given the t-value or t- table. The critical t-value is dependent on the confidence interval you want to achieve, for example 95% with a P < 0.05 has a t-value of 2.045

If we are given the following example:

Mean = 122

SD = 9

n (number of observations) = 30

Degree of freedom = 30-1 = 29

t (look-up, two-tailed) = 2.045 (for 95% CI, P < 0.05)

SEM = 9/√30 = 1.64

95% CI = 122 - (2.045×1.64) = 119 to 122 + (2.045×1.64) = 125

95% CI = 119 to 125.

We can now say, from our given sample, we are 95% confident that the true population mean lies between 119 and 125.

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