Every Three Zebra Stripes

Zebra striping provides a visual guide for the eye as it scans along a row in a table; helping avoid confusion with adjacent rows. But there's more than one way to skin a zebra...

Do we need it at all?

As a quick aside, there was recently an article by Jessica Enders on A List Apart describing the results of a study into the effectiveness of zebra striping. As someone pursuing a degree in psychology this is right up my alley, so I found it somewhat interesting. However, it is worth noting that conclusions built on a single study are rarely that conclusive (especially initial studies since they tend to have flaws in their design). Conclusions that we can actually make use of tend to happen over the course of a series of experiments. This is one reason why main-stream-media science reporting is usually so awful. So take it for what it is.

One thing the study does reinforce is that we really don't need zebra striping on every table. Narrow tables, for example, don't require them since the fovea can take in the whole row without scanning. In contrast, tables with missing data may have a greater requirement for it since the text no longer acts as such a clear visual guide.

Wide Stripes

Zebra striping typically alternates the stripes on every row. However, each row tends to be pretty small in terms of height, so scanning is still relatively slow. The tightness of the stripes also draws more attention to itself causing us to shift to the more dominant colour. (fig 1)

fig 1: Striping on every row gives the eye a narrow track to run down.

An alternative is to stripe on every three rows. This gives us a much larger band for our eye to stay within so we should be able to scan quicker. Three is an optimal number because it provides us with an additional guide: a row is either at the top, middle or bottom of the zebra band. (fig 2)

fig 2: Striping on every third row gives a much larger track. Orientation on the individual row is further aided by recognising that the row is either at the top, middle or bottom of this track.

False meaning

One potential issue here is that the stripes create groups. Some may look for meaning in this grouping, believing it to be more than just a visual guide.

For this reason, in cases where there are natural groups, it may be best to stripe according to these.

One design I have seen is an inconsistent striping pattern. For example, 3 rows grey, 2 white, 3 grey, etc. This always leads me to look for groups that don't actually exist, so I suggest keeping it consistent.