From the results of this year’s high-school “maturity exam” in Poland (courtesy of reader Artur Janc), comes this histogram showing the distribution of scores for the required Polish language test, which is the only subject that all students are required to take, and pass.
Not quite a normal distribution. The dip and spike that occurs at around 21 points just happens to coincide with the cut-off score for passing the exam. Poland employs a fairly elaborate system to avoid bias and grade inflation: removing students’ names from the exams, distributing them to thousands of teachers and graders across the country, employing a well-defined key to determine grades. But by the looks of these results, there’s clearly some sort of bias going on.