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).

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/

Citation count in each year was normalized to the maximum citation counts of the time period. The equation $C_{i}^{Norm}=\frac{C_{i}}{C^{max}}$ was used to calculate the normalized citation in a year, in which $C_{i}$ is the citation count in year i and $C^{max}$ is the maximum number of citations in the 5-year time period. As the normalized citation count is not enough to look at the trends of citations before and after the inclusion year, propensity was also calculated. To do this, $R_{i}^{Norm}$, the normalized random citation count was first calculated using the equation $R_{i}^{Norm}=\frac{R_{i}}{R^{max}}$ in which $R_{i}$ is the random citation count in year i and $R^{max}$ is the random maximum citation count in the 5-year time period. This was then used to calculate propensity through the equation $P_{i}=\frac{C_{i}^{Norm}}{R_{i}^{Norm}}$. When $P_{i}$ is equal to 1, the citation count of the articles is what is expected by chance. When $P_{i}$ is greater than 1, the citation count is greater than what is expected, and when $P_{i}$ is less than 1, the citation count is less than what is expected.

Impact of Wikipedia on citation count analysis method

Impact of Wikipedia on citation trends figure

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.

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