The shelf life plot shows the change in the response over time. The plot also shows the estimated shelf life.

If batch is a random factor or is not included in the final model, then Minitab displays a single plot that shows all batches. If batch is a fixed factor and is included in the final model, then you can specify how many batches to show on the combined plot and whether to show individual plots for each batch.

Plots for individual batches show the shelf life for the specific batch. Combined plots show the overall shelf life.

The combined shelf life plot for the pill data shows that the drug concentration decreases over time. The solid lines represent the fitted regression line for each batch. The dashed lines represent the 95% lower confidence bound (LB) for the mean. The shelf life for this analysis is estimated as the time at which the lower bound for the worst batch, Batch 2, reaches the lower specification limit (LS) of 90. This occurs at 54.7898 months.