1. The problem statement, all variables and given/known data I am needing to identify whether or not my distribution follows a normal distribution. Now by eye it kind of looks like it does, but I need to perform the kolmogorov-smirnov goodness-of-fit test to verify this. Below is a picture of my dataset with a normal curve fitted to it (red line is the normal curve). http://img79.imageshack.us/img79/6730/statsis9.jpg [Broken] 3. The attempt at a solution So anyway to test this I was using the "kstest" function in Matlab. I essentially have 13 million data points and when I test this I get H=1, which means that the null hypothesis (that the distribution DOES follow a normal distribution) has been rejected. However, when I only use 1000 data points it returns the value of H=0, which means that the null hypothesis has been accepted. I was just wondering if anyone knew why this would be so and if you maybe had any recommendations on what I should do? Appreciate any advice. Thanks.