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| DOCUMENT NO.: III-04 | VERSION NO.:1.2 | Section 4 - Basic Statistics and Presentation | EFFECTIVE DATE: 10/01/2003 | REVISED: 06/27/2008 |
4.5 Development and Validation of Spreadsheets for Calculation of Data
When using spreadsheets or programmable calculators for reduction of data
generated by sample analyses, there should be assurance that the results are
valid and usable for regulatory use. The following section provides guidance
for assuring that spreadsheets will meet these criteria.
4.5.1 Introduction
Although the formulas given above for calculation of statistical parameters
may seem complicated, matters are simplified by the ready availability of spreadsheets
and calculators which provide these values transparently. This makes calculation
of statistical parameters much more straightforward than in the past, when
direct application of these formulas was used. It is still useful to have some
familiarity with these formulas to understand how statistical parameters are
derived. In addition, there may be a need to verify the results of statistical
data generated by a spreadsheet or calculator; data can be plugged directly
into the formulas above to verify these results.
4.5.2 Development of Spreadsheets
Excel® and other spreadsheets incorporate all of the statistical parameters
discussed, as well as many others. Although individual spreadsheet functions
can be considered as reliable, it is important to make sure that data is presented
to the spreadsheet with the proper syntax. Also, when spreadsheets are used for
multiple numerical calculations in the form of in-house developed templates,
it is important to protect the spreadsheet from inadvertent changes, to verify
the reliability of the spreadsheet by comparison with known results from known
data, and to ensure that the spreadsheet can handle unforeseen data input needs.
Spreadsheets developed in the ORA laboratory should be looked upon as in-house
developed software that should be qualified before use, just as instruments are
qualified before use.
4.5.3 Validation of Spreadsheets
General guidance for design and validation of in-house spreadsheets and other
numerical calculation programs includes the following considerations:
- Lock all cells of a spreadsheet, except those needed by the user
to input data.
- Make spreadsheets read-only, with password protection, so that only
authorized users can alter the spreadsheet.
- Design the spreadsheet so that data outside acceptable conditions
is rejected (for example, reject non-numerical inputs).
- Manually verify spreadsheet calculations by entering data at extreme
values, as well as at expected values, to assess the ruggedness of the spreadsheet.
- Test the spreadsheet by entering nonsensical data (for example alphabetical
inputs, <CTRL> sequences, etc.).
- Keep a permanent record of all cell formulas when the spreadsheet
has been developed. Document all changes made to the spreadsheet and control
using a system of version numbers with documentation.
- Periodically re-validate spreadsheets. This should include verification
of cell formulas and a manual reverification of spreadsheet calculations.
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