Enter the dependent and independent variables in the calculator, and the tool will determine the prediction interval range.
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The prediction interval calculator estimates the confidence interval for a future observation of a dependent variable (Y) given a set of independent variable (X) values. It is especially useful in regression analysis to determine the expected range for a new observation.
A prediction interval defines a range within which a future observation is likely to fall. For example, a 95% prediction interval of [5, 10] means you can be 95% confident that the next observed value will lie between 5 and 10.
Independent (X) and dependent (Y) variable observations:
| Obs. | X | Y |
|---|---|---|
| 1 | 6 | 14 |
| 2 | 7 | 15 |
| 3 | 7 | 15 |
| 4 | 8 | 17 |
| 5 | 12 | 18 |
| 6 | 14 | 18 |
| 7 | 15 | 16 |
| 8 | 16 | 14 |
| 9 | 16 | 11 |
| 10 | 19 | 8 |
The standard error of a predicted value at a specific \(X_h\) is:
\(SE_{\hat{Y}_h} = \hat{\sigma} \sqrt{1 + \frac{1}{n} + \frac{(X_h - \bar{X})^2}{SS_{XX}}}\)
For example, for \(X_h = 15\):
\(SE_{\hat{Y}_h} = 2.9324 \sqrt{1 + \frac{1}{10} + \frac{(15 - 12)^2}{196}} \)
\(= 2.9324 \sqrt{1 + 0.1 + 0.0459} \)
\(= 2.9324 \sqrt{1.1459} \approx 3.136\)
For a 95% confidence level with \(n-2 = 8\) degrees of freedom:
\(t_{0.025,8} \approx 2.306\)
\(E = t \times SE_{\hat{Y}_h} = 2.306 \times 3.136 \approx 7.232\)
\(\hat{Y}_h \pm E = 13.651 \pm 7.232\)
So, the 95% prediction interval is approximately:
[6.419, 20.883]
Using the regression calculator, the predicted value is \(\hat{Y} = 17.4467\) and the margin of error \(E = 7.7916\):
\(PI = [\hat{Y} - E, \hat{Y} + E] = [9.6551, 25.2383]\)
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Output:
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