erm  i don't know that's, this is not in any official stats books but it's just my experience with students' projects that if you get more than, there's a sort of critical mass of about, about forty respondents and then you're much more likely to start showing some interesting statistically significant findings for some reason, erm i don't quite know why but er   it's one of life's little mysteries but er so that's  usually if there's a lot of numerical data what i'd try and advise people to er to get.