Shelf life for Stability Study

Shelf life plot

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.

Shelf life estimates table

By default, the shelf life when batch is a fixed factor is the time period in which you can be 95% confident that at least 50% of the response is within specifications. When batch is a random factor, the default shelf life is the time period in which you can be 95% confident that at least 95% of the response is within specifications. You can change the confidence level and the percent to make the analysis more or less rigorous. For more information, go to Select the options for Stability Study.

Interpretation

If the batch factor is not included in the final model, then the shelf life is the same for all batches. Otherwise, the shelf life for each batch is different. For a fixed batch factor, Minitab displays a shelf life estimate for each batch. For a fixed batch factor, the overall shelf life for the product is equal to the smallest of the individual shelf life values. For a random batch factor, the estimate of the shelf life accounts for the variation among batches and could be less than or greater than the shelf life for the smallest of the individual shelf life values.

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