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  • Glossary

Errors

If you have a data set for which you already know the correct ordering and/or some dates, you can see how good a job OptiPath does in seriating. OptiPath simplifies this by computing errors for you. Normally this is of no use but we included it so we could test how good a job OptiPath, and the various seriation techniques, really do. The Errors report allows users to test the effectiveness of OptiPath by seriating a set of items whose order and dates are known. To use the Errors function the user must enter the correct seriation ordering in the Index field and/or the correct dates in the Earliest and Latest date fields in the Artifacts (Assemblages) table (the Index can also be edited in the Data table). OptiPath computes date errors only for artifacts or assemblages for which Use Dates has been selected on the Artifacts/Assemblages table.

Errors can be viewed in the Seriations table.

Date Error is the average error in the seriation for items with user supplied dates. If the user enters an Earliest and/or Latest date for an item (an artifact or assemblage), OptiPath compares the date of an item computed by OptiPath with the user supplied dates.

Order Error is the average order error in the seriation. To compute errors, OptiPath compares the Index of an item with the Order computed by OptiPath.

% Date Error is the average percentage error in the seriation for items with user supplied dates. If the user enters an Earliest and/or Latest date for an item (an artifact or assemblage), OptiPath compares the date of an item computed by OptiPath with the user supplied dates and express the difference as a percentage of the allowed range of dates in the seriation (determined by the difference between the Earliest and Latest dates for the Seriation).

% Order Error is the average percentage error in the seriation. To compute errors, OptiPath compares the Index of an item with the Order computed by OptiPath and express the difference as a percentage of the range of ordinal positions in the seriation, which is just the number of items included in the seriation minus one. A random seriation would be expected to have normalized errors of about 33.3%.

Selecting Show Errors on the Results menu will bring up the Errors dialog.

Order Error is an indication of how good a job OptiPath has done in ordering the items (artifacts or assemblages) in your seriation. To compute Order Errors, OptiPath compares the Index of an item with the Order computed by OptiPath. The Raw numbers reported are the average values of the absolute values of the differences between the computed numbers and the input numbers. The Normalized numbers are the same values expressed as percentages. The normalized order error is expressed as a percentage of the range of ordinal positions in the seriation, which is just the number of items included in the seriation minus one. If the Index numbers for the items being seriated are not the correct ordering, the errors analysis is meaningless. A random seriation would be expected to have normalized errors of about 33.3%.

Date Error is an indication of how good a job OptiPath has done in ordering the items (artifacts or assemblages) in the seriation. To compute Date Errors, OptiPath compares computed date of an item with the user entered Earliest and/or Latest date for the item. The Raw numbers reported are the average values of the absolute values of the differences between the computed dates and the input dates. The Normalized datesare the same values expressed as percentages. The normalized date error is expressed as a percentage of the overall allowed date range of the seriation, as determined by the Earliest and Latest dates for the seriation. If the Earliest or Latest dates for the items being seriated are not correct, the errors analysis is meaningless.