What do the triangle/wing tips mean on the anova1 boxplots? I know the line in the middle is the median, the box goes out to the 25th and 75th percentile, the lines extend to the most extreme values not considered outliers and then outliers are plotted as separate points. What I want to know is why the middle portion is not a simple rectangular box.
MATLAB: What do the triangular sections mean on anova1 boxplots
anova1boxplottriangle tips
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It's not a dumn question. Matlab's documentation can be thin when it comes to statistical methods - even when those methods are engrained into their built-in functions.
The notches on the sides of a box plot can be interpreted as a comparison interval around the median values. The height of the notch is the median +/- 1.57 x IQR/sqrt(n) where IQR is the interquartile range defined by the 25th and 75th percentiles and n is the number of data points [1]. If the notches of two boxes do not overlap, there is strong evidence that their medians "significantly differ"[2], a phrase that is working its way out of statistics [3].
The reason why your notches extend beyond the 25th and/or 75th percentiles is due to the uncertainty of the true median value. This often happens if your sample size is small (because you're dividing by the sqrt(n) to calculate the notch height).
image above: [2]
To apply that to your box plots:
Update: a pictoral explanation of boxplot notches has been added to Matlab's documentation [4,5].
Solved by putting
set(gca,'xticklabel',{''})after the openfig command. For some reason removing the labels using set(gca,'xticklabel',[]) wouldn't work
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