Interpret the key results for Predict for Stability Study

Complete the following steps to interpret a stability study. Key output includes the regression equations, fitted values, confidence intervals, and prediction intervals.

Step 1: Examine how the term is associated with the response

Minitab displays the equations that it uses to calculate the predicted values (also called fits) for the response.

Regression Equation Batch 1 Drug% = 99.853 - 0.090918 Month 2 Drug% = 100.15 - 0.16047 Month
Key Result: Regression equations

In these results, the predicted values from Batch 1 are calculated using the equation, Drug% = 99.853 - 0.090918 Month. The slope for Batch 1, 0.090918, is less steep than the slope for Batch 2, 0.16047, which indicates that the concentration of Batch 1 decreases more slowly than the strength of Batch 2.

Step 2: Estimate the mean response

The confidence intervals are the range in which the estimated mean response for a given set of predictor values is expected to fall. The interval is defined by lower and upper limits, which are calculated from the confidence level and the standard error of the fits.

Settings Variable Setting Month 54.79 Batch 2 Prediction Fit SE Fit 95% CI 95% PI 91.3609 0.801867 (89.7233, 92.9986) (89.3217, 93.4001) XX XX denotes an extremely unusual point relative to predictor levels used to fit the model.
Key Result: Confidence interval

In these results, you can estimate with 95% confidence that the mean drug concentration for Batch 2 at 54.79 months is between approximately 89.7% and 93.0%.

Step 3: Estimate the predicted response

The prediction interval (PI) is the range in which the predicted response for a single observation with a given set of predictor values is expected to fall. The interval is defined by lower and upper limits, which are calculated from the confidence level and the standard error of the prediction. The prediction interval is always wider than the confidence interval because of the added uncertainty involved in predicting a single response versus the mean response.

Settings Variable Setting Month 54.79 Batch 2 Prediction Fit SE Fit 95% CI 95% PI 91.3609 0.801867 (89.7233, 92.9986) (89.3217, 93.4001) XX XX denotes an extremely unusual point relative to predictor levels used to fit the model.
Key Result: Prediction interval

In these results, you can state with 95% confidence that the predicted concentration for a single pill from Batch 2 at 54.79 months is between approximately 89.3% and 93.4%.

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