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The data plotted above are from the "MSLQ" study mentioned in Chapter 9 of your
favorite read, the Lertap manual.
Results from one of the MSLQ scales, "SelfReg", have been plotted for three groups of
student teachers: ECE (Early Childhood Education), Primary, and Secondary.
The top of each box corresponds to "Q3", the 75th percentile; the bottom of each box
corresponds to "Q1", the 25th percentile. The line in the middle of each box represents
the position of "Q2", the median, the 50th percentile.
Shouldn't the median be halfway between the 75th and 25th percentiles? If the
distribution of scores is symmetric, yes, but otherwise no. ("Otherwise" is the usual
case as scores are not often exactly symmetric about the median.)
The lines sprouting from the top and bottom of each box are the "whiskers". The top
whisker extends from the 75th percentile, Q3, to the highest score which is not an
"outlier". Similarly, the bottom whisker extends from the 25th percentile, Q1, down to
the lowest score which is not an "outlier". Outliers are discussed below.
A plot such as the one above has a lot of information. The Primary students tended to
have higher SelfReg scores, and the range of their scores was the greatest: the P
group's whiskers extend a bit further than those for the other groups.
The highest median score is found in the P group.
The SelfReg scores of the Secondary students are, by and large, the weakest: their
median score and their "Q1" score are lowest of the lot.
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