Hi, first you have to check which type of distribution you have. E.g. you can check via QQ-plot if your data (for each man) are normally distributed. If your data are normally distributed, you can calculate the mean value of the hairs of each man, leading to 10 values M1,..,M10. Now you can calculate their Mean M and variance V, the squareroot of the variance sqrt(V) is the standard error SE of the average hair length M. 95%-CIs are now computed via: [M-1.96*SE,M+1.96*SE]. Ist this what you want? However, these calculations assume that data are normally distributed, as mentioned above, this has to be proven. Best, mmercker