The dissemination of divination in roman republican times

The number of prodigies for each named location was summarized 210 and the beeline distance
from this location to Rome was measured based on the map in Putzger Historischer Weltatlas
(Putzger, Hansel, & Leisering 1961). We could have taken the raw correlation between number
of prodigies for each location and its distance to Rome, but we are not interested in exact
distance, and single observations from close by places would have skewed the data: if we had
observation of a single prodigy from 10 different places very close to Rome and only one
kilometer apart, and a few from one place 500 kilometers from Rome the correlation coefficient
would appear mathematically to indicate a function linearly increasing with distance although
the reverse is true. In order to avoid this, the observations were grouped in ranges of 25
kilometers. That would also have been more in accordance with the perceptions of the Romans:
they would not have taken out a map and measured the precise distance, but rather have made a
loose assessment of distance. In the context of ancient Roman transportation 25 kilometers
would have been a salient difference in distance. In consequence a measure of distance based on
ranges of 25 kilometers appears to be a better measure than exact distance. The number of
prodigies in each 25 kilometer zone will then be summarized.
The distances for each observation were recoded into a variable designating the range. Thus
the range 0-25 km was recoded as 1, 26-50 km as 2 and so forth. There were three outliers (more
than 500 kilometers away). They were from Syracuse, Croton and Etna. They were excluded
since they were most likely omens. 211 Their inclusion would, however, not change the
conclusion. The number of prodigies for each range was summarized. A scatter plot with
distance by range on the abscissa and summarized number of prodigies for each range on the
ordinate indicated a possible logarithmic function, why a regression analysis for a linear as well
as a logarithmic model was made. The R square for the linear model was 0,53, which is
significant (p