Frequency seriation is a special case of Shortest Path seriation where the feature values for an item (artifact or assemblage) are non-negative fractions and add up to zero or one. The seriation Technique can be set in the Seriations table. If you choose Frequency seriation, OptiPath will automatically convert the Values of your data to non-negative fractions summing to one (or zero, if all data for an artifact or assemblage are zero or unknown). To see the effect on the raw data, look at processed data in the Values table.
Frequency seriation is often used when we have raw data for individual artifacts that can be aggregated into assemblages. Feature data for the assemblage then reflect the fraction (percentage) of artifacts in the assemblage that share a common trait (style, class or feature value). By treating each assemblage as an artifact, and each trait as a feature, frequency seriation is a special case of shortest path seriation. However, it is not necessary to use assemblages to use frequency seriation.
The underlying assumption in frequency seriation is that a feature will normally be introduced only once in the evolution of a feature value or style - once the feature has appeared and then been absent in artifacts for a period of time it will not reappear, and that the frequencies of the individual features will tend to change slowly and smoothly over time. Most implementations of frequency seriation attempt to order the artifacts temporally so as to minimize the number of times that a distinct feature is introduced into the archaeological record (transitions from absent to present, and present to absent) and so as to minimize the number of reversals from increasing to decreasing, or vice versa, of the individual feature's frequency.
Frequency seriation is a special case of the Optimal Path seriation model. Setting the Seriation parameter Technique to Frequency specifies OptiPath's standard implementation of frequency seriation. Data may take on any numerical value. Positive numerical values are converted to frequencies. Negative values, zero values and non-numerical values, including blanks, are treated as absent and zero, resulting in a zero frequency. Setting the seriation parameter Technique to Frequency causes OptiPath to automatically set the feature parameters Data, Ranks, Metric, Normalize, Transition, Earlier, Later, Blanks and Zeroes to specific values.
The following are the default feature parameter settings for frequency seriation. To change them you must first select the Custom Seriation technique.
| Parameter | Value |
| Data | Measured |
| Ranks | 0 |
| Metric | Euclidean |
| Normalize | No |
| Transition | 0 |
| Earlier | Unknown |
| Later | Unknown |
| Blanks | Absent & Zero |
| Zeroes | Absent & Zero |
These settings result in any numerical entry in the Data being interpreted as indicating the presence of a feature (class or style). If you do not want blanks or zeroes to be interpreted in this way, you should set the seriation parameter Technique to Custom and reset the feature parameters Blanks and Zeroes. To see the effect of your settings, look at processed data in the Values table.
In frequency seriation, careful thought should be put into setting the feature parameters appropriately - see Setting the Earlier, Later, Blanks, Zeroes and Transition Parameters.