To determine the prevalence of plagiarism among medical students in writing essays. During two academic years, 198 second year medical students attending Medical Informatics course wrote an essay on one of four offered articles. Two of the source articles were available in an electronic form and two in printed form. Two (one electronic and one paper article) were considered less complex and the other two more complex. The essays were examined using plagiarism detection software "WCopyfind," which counted the number of matching phrases with six or more words. Plagiarism rate, expressed as the percentage of the plagiarized text, was calculated as a ratio of the absolute number of matching words and the total number of words in the essay. Only 17 (9%) of students did not plagiarize at all and 68 (34%) plagiarized less than 10% of the text. The average plagiarism rate (% of plagiarized text) was 19% (5-95% percentile=0-88). Students who were strictly warned not to plagiarize had a higher total word count in their essays than students who were not warned (P=0.002) but there was no difference between them in the rate of plagiarism. Students with higher grades in Medical Informatics exam plagiarized less than those with lower grades (P=0.015). Gender, subject source, and complexity had no influence on the plagiarism rate. Plagiarism in writing essays is common among medical students. An explicit warning is not enough to deter students from plagiarism. Detection software can be used to trace and evaluate the rate of plagiarism in written student assays.
