Hi As Rick points out, the number of students is largely irrelevant to whether you get a normal distribution, unless you know (think) you're sampling from a normal distribution to begin with.
Where number of observations comes into play is if you are calculating a sum or average of the observations to create scores that are then analyzed and plotted. Here the more individual observations going into each score will contribute to the normality of the resulting scores, (almost?) irrespective of the original distribution of raw observations. Take care Jim Jim Clark Professor & Chair of Psychology 204-786-9757 4L41A From: [email protected] [mailto:[email protected]] Sent: Friday, November 22, 2013 1:23 PM To: Teaching in the Psychological Sciences (TIPS) Subject: [tips] Sample size for normal assumption Paul Brandon asked for stats mavens to address his inquiry: "How many students do you need to justify the assumption of a normal (or other) distribution of measures of performance?" -------------------------- If you know any mavens, you may suspect that they will not have a simple answer for him. :) There isn't a particular number that will ensure a normal distribution if the population isn't normally distributed in the first place. Probably the closest a college class would come to the normal distribution of raw scores concerning knowledge of an academic subject would be in an Intro class required of all majors. Even then, distributions are often bimodal. Once you get to upper division major classes, it is very difficult to justify the expectation of a normal distribution, no matter how many students may be in a class. Of course, there are always exceptions (which is where the mavens come in...). Rick Dr. Rick Froman, Chair Division of Humanities and Social Sciences Professor of Psychology Box 3519 John Brown University 2000 W. University Siloam Springs, AR 72761 [email protected]<mailto:[email protected]> (479) 524-7295 http://bit.ly/DrFroman "The LORD detests both Type I and Type II errors." Proverbs 17:15<http://www.biblegateway.com/passage/?search=proverbs%2017:15&version=NIV> --- You are currently subscribed to tips as: [email protected]<mailto:[email protected]>. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13251.645f86b5cec4da0a56ffea7a891720c9&n=T&l=tips&o=30450 (It may be necessary to cut and paste the above URL if the line is broken) or send a blank email to leave-30450-13251.645f86b5cec4da0a56ffea7a89172...@fsulist.frostburg.edu<mailto:leave-30450-13251.645f86b5cec4da0a56ffea7a89172...@fsulist.frostburg.edu> --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13090.68da6e6e5325aa33287ff385b70df5d5&n=T&l=tips&o=30468 or send a blank email to leave-30468-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
