Estimating the Probability of Accidental Extinction Using Excel*

Current version: February 15, 2013

An Excel workbook is used to estimate the probability of accidental extinction of an organismic population from its fluctuating count record assuming the counts have a normal or lognormal distribution. It can also be used to estimate the probability of encountering counts of probiotic mirobes or spores in industrial products that are below specified thresholds.

The pop-up comment notes from the worksheet are also available on this page so that you may read and/or print them before using the worksheet.

The workbook includes a plot of the data and two histograms (one of the entered data and the other after their logarithmic conversion), the calculation and plotting of the autocorrelation function and the Quantile-Quantile plots of the normal and lognormal distributions to help the user decide which one better represents the data. An 'Update Worksheet' button runs a Visual Basic macro to automatically update any cells and charts in the worksheet that are affected by changes in the count data. You must click on the 'Enable Macros' button in the dialog box that is displayed before the worksheet opens in Excel in order for the macro to be useable.

* Excel® is a registered trademark of Microsoft Corporation. You can get more information about Excel by visiting Microsoft's web site at:

Download the Demonstration Excel Worksheet File

The Excel worksheet (EstimatingProbabilityOfAccidentalExtinction.xls) is available in the file format of Excel 97 through 2003 for Windows and Excel 98 through 2004 for MacOS. If you have a modern web browser you should be able to download the binary Excel file directly by clicking on the link below. If a compatible version of Excel is currently installed on your computer, double-click the icon for the EstimatingProbabilityOfAccidentalExtinction.xls file that was downloaded to open the worksheet in Excel. Be sure to click the 'Enable Macros' button in the dialog box that appears. If you are using a recent version of Excel for Windows, you may need to first reduce the security level in Tools>Macro>Security to Medium, then close and reopen the file to enable the macros.

For Windows and MacOS:
Excel binary file (262K) for Windows Excel 97 through 2003 and MacOS Excel 98 through 2004: EstimatingProbabilityOfAccidentalExtinction.xls

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Content last updated: February 15, 2013