# How to label a constant y-axis in a grid of plots?

I have a grid of plots (see example below) with different x axes but all the same y-axis. What is the best way to label the y-axis without being redundant? The information is in the legend, but this is not a solution.

Here are two options I am considering:

• center one label on the right hand side in the same font as the x-axis labels. This could make it ambiguous if the y-axis label is associated with only one subplot.
• leave the y-axis empty and provide information in a figure title (response of 'y-axis label (units)' to 15 variables).

This plot will be published in a scientific journal. Low resolution is intentional for this post since it is unpubliished. Any other suggestions appreciated.

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I do not see any problem with this, as long as the label is not pneumonoultramicroscopicsilicovolcanoconiosis. You can find many examples like this in AoAS. I would be more worried about the grid not being too bold. Another option is to specify the meaning of the $y-$axis in the caption. –  user10525 May 23 '12 at 18:45
@whuber thanks for the examples, they are more clear than I had imagined. –  David May 23 '12 at 21:19
In case you want more, I found them with a Google image search for "R trellis graphics". You have to be choosy, though: evidently, most statistical graphics one finds on the Web are awful :-). –  whuber May 23 '12 at 21:23
@whuber I also found quite a few copies flipping through a stack of actual bound journals that ended up in the recycling bin. The y-axis label seems to do fine, and it is nice not to have to read the legend. –  David May 23 '12 at 21:42
@Jake It is not clear that it would make the plots easier to digest. My assumption is that it would takes up space and be distracting. If I saw sixteen y-axis labels, I would assume that they did not all contain the same information. –  David May 23 '12 at 22:55