Prediction Interval
We would like to construct a prediction interval around which would contain the actual Y.
If n ≥ 30, ± Zs_{e} would be the interval, where Z is the appropriate Standard Normal Value.
If n < 30, ± ts_{e} would be the interval, where t is the appropriate t value (with n - 2 degrees of freedom).
In the case of the pharmaceutical firm, at X = Rs.1 crore the 90% prediction interval is 22 ± 2.132 x 3.24.