This paper presents: (I) an historical review of the development of Malecot's isolation by distance model. (2) a synthetic summary of empirical results from four major components of the middle Dalmatian population system, (3) a novel table of "critical" values of Malecot's parameter "b" to aid in the interpretation of isolation by distance effects, and (4) a simulation study designed to analyze the power of the quadratic assignment procedure for testing the significance of Pearson's product-moment and Spearman's rank-order correlation coefficients. Statistically significant regressions resulted in 26 estimates for 'b" (mean - 0.112) and 16 estimates for "a" (mean - 0.0044) from our middle Dalmatian applications of Malecot's model. These values indicate that both long-range and short-range migration are important components of middle Dalmatian population structure. Analysis by data set type led to the conclusion that linguistic distances and migrational kinship generally fit the isolation by distance model better than more strictly biological traits. Among the biological data sets anthropometrics fit the model better than physiological, dermatoglyphic or radiogrammetric metacarpal data. The simulation study employed a rectangular area which approximated the geography of our empirical population system and required the addition of a normally distributed random error term, U(E), to the Malecot model in order to examine the power of the permutation tests under the hypothesis of isolation by distance. When the error term is not present, the power of both the Pearson and Spearman tests is 1.00 for all values of "b" and "a". When the error term is present, Pearson's test is generally more powerful than Spearman's; however, with increasing values of "b", the permutation tests for both coefficients rapidly loses its power. We conclude that the quadratic assignment lest for Pearson's product-moment correlation coefficient is satisfactory only for values of "b" and "E" < 0.10. For these values, Pearson's test is more powerful than Spearman's and such values of "b" are frequently found in the literature with the upper bound actually lying between the mean and median for our 26 middle Dalmatian "b" values based on significant regressions of biological (sociocultural) distances on geographic distance