Propensity was calculated for each year for each of subcategory of articles analyzed. It can be seen that inclusion of an article does not increase propensity, meaning an article is not cited more after it is referenced in Wikipedia.

University of California, Berkeley

This study tested the hypothesis that references to an article in Wikipedia affects the article's citation trends. A measure citation "propensity" was created, which measures the likelihood of an article being cited more than what is to be expected by chance. Using statistics in the Scopus database and this measure, it was found that while the number of citations to an article does increase in number over time, citation propensity does not increase for an article after it is referenced in Wikipedia, meaning that references to an article in Wikipedia does not affect the article's citation trends. 

Impact of Wikipedia on citation trends

Marashi, S. A., Hosseini-Nami, S. M. A., Alishah, K., Hadi, M., Karimi, A., Hosseinian, S., ... & Shojaie, Z. (2013). Impact of Wikipedia on citation trends. EXCLI journal, 12, 15.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4803015/

Normalized citation count of the articles was calculated for each year. Two years before the article was included in Wikipedia and two years after were looked at. It can be seen that there is a general trend of increase in citations after each year, but not necessarily after the inclusion year (year 0).

Impact of Wikipedia on citation trends figure

Citation counts for each year were normalized to the maximum citation count of the time period using the equation $$C_{i}^{Norm}=\frac{C_{i}}{C^{max}}$$, where $$C_{i}$$ is the citation count in year $$i$$ and $$C^{max}$$ is the maximum citations in a 5-year period. To evaluate trends before and after Wikipedia inclusion, a 'citation propensity' metric was utilized. First, the normalized random citation count ($$R_{i}^{Norm}$$) was calculated as $$R_{i}^{Norm}=\frac{R_{i}}{R^{max}}$$, where $$R_{i}$$ is the random citation count in year $$i$$ and $$R^{max}$$ is the random maximum citation count in the 5-year period. Finally, propensity was calculated as $$P_{i}=\frac{C_{i}^{Norm}}{R_{i}^{Norm}}$$. A propensity ($$P_{i}$$) equal to 1 indicates the citation count matches chance expectations, greater than 1 indicates higher than expected citations, and less than 1 indicates lower than expected citations.

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