Confidence Interval
This parameter indicates the percentage confidence that the true value of the mean, for the population or quantity being sampled, lies within the stated interval.
The confidence interval will tend to narrow for sample data that have a small standard deviation and as the number of data samples (elements) increases.
The Calculator uses the following formula in its calculations:
Confidence interval = [
- z
/
n, + z/n]
Where:
= the sample mean
= the standard deviation of the sample
n = the number of data elements (samples)
Z = the value from the table below
|
Z ( 0.1 ) |
Z ( 0.05 ) |
Z ( 0.025 ) |
Z ( 0.01 ) |
Z ( 0.005 ) |
Z ( 0.001 ) |
Z ( 0.0005 ) |
|
1.282 |
1.645 |
1.960 |
2.326 |
2.576 |
3.090 |
3.291 |
Example:
For the confidence limit of 90%, the Z ( 0.05 ) value is used in the above equation to calculate the interval; for the 99% confidence limit, the Z ( 0.005 ) value is used.