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Statistics

This screen presents some simple statistics about data that have been stored.
Statistics are calculated on the current list of S.U. If no filter is applied to the list, statistics are calculated on the whole dataset of the intervention; if the list has been filtered, only this filtered sub-set of data is considered.

The report can be saved to a text file. It will be stored in the same folder of the intervention file, with a name formed by the intervention name plus the postfix "_stats".
Subsequent "stats files" will overwrite the last one without prompting, so rename and/or move the file if you believe you will use it further.

At the moment, statistics concern basically two types of data: count of S.U. and volume of S.U., both grouped by type of S.U. (positive/negative) and chronological periods. The report include also a "ILIUM Minimum Accuracy Level" value.

The latter is a sort of index that evaluates the accuracy of the documentation, based on a number of fields that have to be filled. The maximum value is 0 (minimum accuracy reached), while values below 0 indicate some lacks in the documentation. Keep in mind that it's just an indicative value, and a result of 0 is given even if only a small set of fields are filled for each S.U. Documentation can be insufficient, under the human point of view, even if the software gives its approval. Each kind of S.U. can have its own characteristic fields (e.g., it's important to register the colour of a layer of soil or of a mortar covering, but usually it's not necessary to specify the colour of a stone wall)

The count of S.U. only has a really small interest, and its utility is just to keep track of the set of records.

Volume, on the contrary, it's a more significant pointer to take in account when interpreting an archaeological site and worth some explication.
It could be view, e.g., as a rough indicator of activity during historic times: at more volume (of buildings, of movement of soil, of holes...), more activity. Obviously the relationship is not so linear, but at a first glance it's a valid preliminary approach.
Also, volume (of layers) can be useful if is used to calculate the concentration of finds embedded in the soil.

The user has to assume that volumes presented in the report usually aren't exhaustive data. Their precision varies according to limitations of the algorithm used, the detail of documentation entered by the user, and others factors.
The software calculates the volume of every S.U. of which have been entered height, length and width, or radius (or diameter) and height.
Volume will be always presented in m3; the software makes opportune transformations if the dimensions entered by the user are stored in units other than meters. But be careful of errors while entering data: if, by mistake, you specify, e.g., "Kg" as units of length, the software will not consider this dimension.
For each dimension, if the "average" value has been introduced by the user, this one will be used by the algorithm; if there is not the average value but there are "max" and "min" values, the program calculate the average by itself; if just a "max" or a "min" dimension is present, it will be used "as is".

This means that:
-The program considers all archaeological elements - including layers of soil - as parallelepiped or cylinders
-Only S.U. with the required dimensions will be taken in account.
-Even for the S.U. that have required dimensions, resulting volume can be an approximation up or down.

To help the user to interpret the report, following is a (fictitious) example of an exported "_stats" text file. Comments are in bold and in square parenthesis.

Start of file
Statistics of file: spain.ilium
at Thu Oct 12 12:24:28 CEST 2017

***OVERALL***:
Total SU: 3
ILIUM 'Minimum Accuracy Level' of documentation: -5.0 [-> Minimum accuracy of documentation not reached]
Total volume: 0.41 m3 [->Total volume (positive and negative S.U.) documented. Take in account that the sum of positive and negative volumes, even if all S.U. were considered, it's not equal to the whole volume of excavation. An hole has a volume (negative), but the soil that fills it has it's own volume (positive) too. Since the two volumes correspond to two different actions, they are both counted.]

***SU GROUPED BY TYPE***:
Positive SU: 2[->number of positive S.U.] (66%[-> percentage on total number of S.U.; in this case it was only 3])
Positive volume calculated on 1 of 2 total positive SU[-> evidently, the user missed to enter required dimensions of one of the two positive S.U.] (50%[->the same, in percentage]): 0.36 m3 [-> volume]

[-> following, the same data for negative S.U.]
Negative SU: 1 (33%)
Negative volume calculated on 1 of 1 total negative SU (100%): 0.05 m3

***SU GROUPED BY PERIODS***:
Roman:
2 [->two S.U.] (66%[->percentage over the total number of S.U.]) SU; 0.36 m3 [->total volume of the Roman activity] (87.8%[->percentage over total volume in all periods. It seems that Romans builded a lot in this site])

[-> following, the same data for all periods]
Medieval:
1 (33%) SU; 0.05 m3 (12.2%)

end of file