Statistics - Field Sampling: Principles and Practices in Environmental Analysis - page 154

TABLE 6.5 Abbreviated Critical Values of t and Q

Percentage confidence intervals for t 90% confidence interval for Q

Q 0.90

n −1 90% 95% 99% 99.5%

1 3.078 6.314 31.821 63.657 —

2 1.886 2.920 6.965 9.925 —

3 1.638 2.353 4.541 5.841 0.941

4 1.533 2.132 3.747 4.604 0.765

5 1.476 2.015 3.365 4.032 0.642

interval is found to be 2.353. Because this value is less than the calculated t the null
hypothesis is rejected. This means that the two means are different and represent two
different populations.
This seems like an obvious outcome because the means are so different. The question
could be asked if areas A1 and C6 are different or the same. Again a null hypothesis is
needed. From Table 6.4 we let the null hypothesis be H 0 : µ =45. (The data are shown in
Table 6.6.) Then the calculation of t becomes

TABLE 6.6 TPH Means and Standard Deviations

Standard deviation a

Sample number Mean (rounded)

A1 44 6

A3 455 49

A4 292 15

A5 165 8

B1 31 1

B2 324 17

B3 1090 100

B4 905 31

B5 717 29

B6 455 25

C5 108 6

C6 51 2

a Truncated

This t -value is smaller than the t -value for the 95% confidence interval, and so the two