21
Compute the upper and lower 95% confidence limits using the
following equations:
Upper Confidence Interval
UCL
=
X
t
s
n
0.05
Lower Confidence Interval
LCL
=
X
t
s
n
0.05
where t can be found in the chart below:
n
t
0.05
15
2.145
16
2.131
17
2.120
18
2.110
19
2.101
20
2.093
21
2.086
22
2.080
23
2.074
24
2.069
25
2.064
Table 1. Values for t
Analysis:
If the reference value is between the lower and upper 95%
confidence limits, the bias is not statistically significant and can be
ignored.
If the reference value is lower than the lower 95% confidence limit or
greater than the upper 95% confidence limit, the bias is statistically
significant and the measurement system must be recalibrated.
