Thanks for all these suggestions. I've been thinking of trying all or most of them. I assume that I would get slightly different results, so let me ask this: what criteria would you use to determine which transformation gave the best result? Would it be the one with the least amount of skew/most normal in distribution?
Michael A. Britt, Ph.D. [email protected] http://www.ThePsychFiles.com Twitter: @mbritt On Nov 11, 2013, at 7:04 PM, Jim Clark <[email protected]> wrote: > Hi > > People have been noting various transformations, depending on reversing or > not the original. In essence many common transformations can be > conceptualized as the original scores raised to various powers, with the > powers being greater than or less than 1. > > x^-1 = reciprocal 1/x > x^~0 = logarithmic > x^.5 = square root > x^1 = original > x^2 = ... > > I'm mostly used to thinking of these in terms of various non-linear > relationships (powers < 1 compress upper end, powers > 1 expand upper end), > but some of these will increase skewness and others will decrease it, > depending on the direction of skew. Possible to experiment with them to > observe effect. > > Perhaps also worth plotting some of the relationships you are interested in? > > Take care > Jim > > Jim Clark > Professor & Chair of Psychology > 204-786-9757 > 4L41A > > -----Original Message----- > From: Christopher Green [mailto:[email protected]] > Sent: Monday, November 11, 2013 5:31 PM > To: Teaching in the Psychological Sciences (TIPS) > Subject: Re: [tips] What to do with skewed data > > Michael, > > There are couple of standard ways to transform skewed data. Invert the data > (subtract each datum from one greater than the highest value) so that the > skew is positive. Then, Depending of the strength of the skew, do a square > root or logarithmic transformation. Alternatively, don't invert it and take > the reciprocal (1/x) of each datum). > > Chris > ....... > Christopher D Green > Department of Psychology > York University > Toronto, ON M6C 1G4 > > [email protected] > http://www.yorku.ca/christo > >> On Nov 11, 2013, at 1:01 PM, Michael Britt <[email protected]> wrote: >> >> I did a survey which asked respondents how satisfied they are in their >> current (romantic) relationship on a 1=10 point scale (where 10="very >> satisfied). While there was some variation, not surprisingly, the results >> are strongly negatively skewed. That makes sense - most people are probably >> satisfied with their relationships or they would leave the other person (or >> there's some form of cognitive dissonance going on, but that's not my >> question. >> >> No matter how big the sample size (mine was 160 respondents) I assume you'll >> always get a skewed distribution on a question like this so wouldn't I be >> breaking the normalization assumption if I were to do correlations using >> these results? I assume I could either do: a) do some kind of >> transformation - but I've never done one before so I’m not familiar with it, >> or b) recode the data into 3 categories (perhaps 1-5 is low satisfaction, >> 6-7 is moderate and 8-10 is high) and do a chi-squre instead of a >> correlation. >> >> Any thoughts? Appreciate it. >> >> Michael >> >> Michael A. Britt, Ph.D. >> [email protected] >> http://www.ThePsychFiles.com >> Twitter: @mbritt >> >> >> --- >> You are currently subscribed to tips as: [email protected]. >> To unsubscribe click here: >> http://fsulist.frostburg.edu/u?id=430248.781165b5ef80a3cd2b14721caf62b >> d92&n=T&l=tips&o=30023 or send a blank email to >> leave-30023-430248.781165b5ef80a3cd2b14721caf62bd92@fsulist.frostburg. >> edu >> > > --- > You are currently subscribed to tips as: [email protected]. > To unsubscribe click here: > http://fsulist.frostburg.edu/u?id=13251.645f86b5cec4da0a56ffea7a891720c9&n=T&l=tips&o=30040 > or send a blank email to > leave-30040-13251.645f86b5cec4da0a56ffea7a89172...@fsulist.frostburg.edu > > --- > You are currently subscribed to tips as: [email protected]. > To unsubscribe click here: > http://fsulist.frostburg.edu/u?id=13405.0125141592fa9ededc665c55d9958f69&n=T&l=tips&o=30042 > or send a blank email to > leave-30042-13405.0125141592fa9ededc665c55d9958...@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=30043 or send a blank email to leave-30043-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
