On 27 Feb 2003 at 22:36, Harris, Betty A wrote: > Hi all, > > While we're talking about outliers I had my first dose of looking at > TerraNova data collected near the beginning of the school year and then > again from the same kids near the end of the school year. We received NCE > scores back on: > Reading Composite > Reading Subtest > Vocabulary Subtest > Word Analysis Subtest > > I calculated gain scores (Spring - Fall) scores for each student. > I was shocked to find that Overall, 23% of third graders (n=113) and 33% of > third graders (n=123) had at least one gain score that was below zero. > > Some lost ground on all three subscales and the composite, however most > students who lost ground between fall and spring testing--65% of second > graders and 62.8% of third graders--only did so on one of the three subtest > scores. Only 5% of second graders and 11.6% of third graders lost ground on > all three subtests. > > To deal with this issue, students with gain scores more than two standard > deviations below the mean gain score were considered outliers and were > removed from the analysis for the subtest with gain scores of more than 2 > standard deviations below the mean gain score for that subtest. > > Does that seem like a legitimate strategy to you?
Do you have any reason to beleave this scores are wrong? Why don't you also remove the ones with gain score more than 2 sd above average? In this case the most important thing one could learn from the data is why so many have negative gain scores, and you are only hiding away what might be the main point of interest in the data. Kjetil Halvorsen > > What about gain scores of more than 2 standard deviations about the mean? > > Out for now, > Betty > > > . > . > ================================================================= > Instructions for joining and leaving this list, remarks about the > problem of INAPPROPRIATE MESSAGES, and archives are available at: > . http://jse.stat.ncsu.edu/ . > ================================================================= . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
