Strange distribution of the 2011 11+ results (statistically)
Posted: Fri Jan 27, 2012 12:43 pm
We are appealing against non-selection and have recently received our case papers, which include everything we sent for the appeal as well as a report on 11+ results in Bucks. Among all other information it have a graph showing the distribution of the results, basically how many students reached any particular score, from 69 up to 141. Overall the results seem to be normally distributed. I mean that the medium/average marks were received by the highest number of students, while the closer the marks to both extremes (69 and 141) the lower number of students received them. That makes sense as the results should be normally distributed. What I cannot understand is that the highest mark (141) has the highest number of students achieving it, which does not make any sense from the statistical point of view. It’s like the 139 mark was achieved by (I do not remember the exact number) 15, students, 140 – by 10 students and 141 by 320 students.
I am sorry if the post is a bit too technical, but what I want to say is that the results around the mean usually achieved by the highest number of people, while the results closer to both ends of the spectre are achieved by less and less people the closer they are to the extremes. So from the statistical point of view there should be should not be this huge difference between how many students got 140 and 141 and the number of the latter should be lower than the former.
Probably there is an explanation for that so I wonder if anyone knows it. Or if the situation was similar in previous years?
I am sorry if the post is a bit too technical, but what I want to say is that the results around the mean usually achieved by the highest number of people, while the results closer to both ends of the spectre are achieved by less and less people the closer they are to the extremes. So from the statistical point of view there should be should not be this huge difference between how many students got 140 and 141 and the number of the latter should be lower than the former.
Probably there is an explanation for that so I wonder if anyone knows it. Or if the situation was similar in previous years?