It gets more complicated and some of our early studies in the late 70's showed that 1`. the design influences how much is written in replies. if the design encourages immediate response like opening a window for the user to type there reply (done today in gmail when you use the slow verison) or when the user has to issue a command to reply then the instant reply was like 5-7 lines and when they had to issue a command it was more like 10-14 almost double. usually that meant they came back and did a reply later which we could tell in those days becuase there was no browser inteh way of tracking the data. however when the reply was made is a factor you want to measure to see if it is any different. If people wait and thnk about it they usually have more to say. some of the early work in this area were in cacm articles by hiltz and turoff back in those days. since i am on vacation i cannot easily reference the other work. remind be after mid sept.l you will need to know how many replies and how many males and females to look at significance tests to see what you can do. first you take the distribution of size of all comments by males and separately all comments by females and do a test to see if it is a normal distribution. If it is for both you can find the easy test to see if the normal has different peaks for each of the two distributions. If it is not normal you need to use non parametric statistical tests. you are also going to have to check the length of time of the creation of the item being replied to and the time interval for each reply. i suspect this will be zipf curve of the frequency of replies over the length of time as will be the number of items over time. That might also lead to some discovery of the older items get the larger they might be which would be interesting to discover and it might be a property of the subject matter. I think some studies by Roxanne hiltz on virtual classroom showed that females made longer comments then males in response to questions and that was correlated with higher verbal test scores they had on entering college. You have to check with her.