*3.3. A Research Method Choice*

The aim of the research was to determine the impact of the electricity consumption profile in the analyzed groups of service enterprises on the cooperation with the National Power System and potential photovoltaic sources. For this reason, the research method was searched for in the group of statistical correlation tests.

Choosing the right statistical test and checking the fulfillment of its assumptions is extremely important from the point of view of the credibility and correctness of the interpretation of the results. The tests of the normality of the distribution are specific tests examining the compliance of a given distribution with the normal distribution the most frequently used in statistics because many features have a distribution similar to it. The assumption that the distribution is normal is often required in the case of parametric statistical tests. Non-parametric tests, on the other hand, are free from such assumptions [52].

The value of the Pearson's correlation score as a measure of the linear relationship between two variables, however, may be underestimated when there is a dependence between the variables, but the relationship is not linear. It may or may not give erroneous values and lead to a misinterpretation of the results if the assumptions about the normality of the distribution are not met.

After initial identification of the lack of a linear relationship between the analyzed variables, higher values in the Spearman's Rho test were expected as a better measure of the degree of correlation of the analyzed variables. The use of non-parametric methods independent of the distribution of the analyzed variables is more convenient from the point of view of meeting the applicability conditions of parametric statistical procedures. Spearman's Rho can be treated similarly to Pearson's linear correlation coefficient, that is, in terms of the percentage of explained variation, with the difference that Spearman's Rho is calculated based on ranks.

As part of the implementation of this study, tests of interdependencies between the variables were carried out using the most intuitive in interpretation parametric test of Pearson's r-correlation and its non-parametric counterpart based on the ranks of the Spearman, the use of which appears to be more adequate [53].
