Tips on examining data: 3 road sign displays

As the old saying goes, “A picture is worth a thousand words.” And when it comes to comparing the performance of various products, graphed data is often an effective means of quickly showing a reader how they stack up, right? Well, maybe not always.

For example, take a look at the graph reproduced below from a sales brochure. Note that the graph is reproduced as it originally appears in the brochure, except that the name of the publisher has been removed.

When presented with data visualized in this way, the common question is “What does the graph show?” But you should also ask yourself, “What does the graph NOT show?” Let’s take a closer look.

After a close inspection, you may be left wondering:
 

1. Which retroreflective sheeting products are represented by this data
2. Are these products directly comparable? Do they belong to the same ASTM D4956 Type or different Types?
3. What are the units of measurement on the horizontal and vertical axes?
4. Why is the spacing on the vertical axis not uniform? (Hint: Using larger increments of space near the top of the graph exaggerates differences.)
5. What combination of entrance and observation angles were used? After all, retroreflective sheeting performance can change dramatically depending upon the angles used in the measurement.
6. Does this data represent performance for the same products at other entrance and observation angle combinations of interest? Or perhaps for all products?
7. If this data shows “normalized” performance, what are the ACTUAL retroreflectivity values for the samples?

The list of questions could go on, but the point is this: a graph may give an impression of performance differences, but it can still fail to provide the whole picture.

After some digging, we found them. This Google Maps link takes you to a ground view of the same signs in the daytime, so you can see for yourself the different angles from the photo could have been taken.

Now, take note where a photographer might have been standing for this angle.
 

• Was the photographer on the main roadway?
• Would a driver on this main highway ever view the sign from this perspective?

Strangely, the photo in question appears that it may have been taken from the frontage road next to the main highway or perhaps from the nearby shoulder. While we can’t make an exact match, we’ve approximated the same pitch and perspective to help provide some context to the photo.

While the photo was intended to reinforce a story about how sheeting orientation affects the appearance of overhead signs, there are inherent problems:
 

• From what perspective was the image taken?
• Is the perspective relevant to drivers?

Just like a fixed road sign, a book conveys information, and is typically read in an upright position.

If you turn a book sideways (change its orientation), it’s harder to read, and is therefore less effective in doing its job (communicating information).

With an “omnidirectional book”—one that would feature new letters and symbols that could be rotated—one could theoretically “spin” it to demonstrate how it could be read from an angle. While this might have a “wow” factor, the question would become: what problem does it solve?

Of course this is a ridiculous example, but it illustrates the false problem of the spinning sign demonstration.

A sign mounted to a post will not spin or blink.

Likewise, when you sit down to read, you position yourself and the book in a fixed position that’s most comfortable for you to read.

Disclaimer: Some photos and reference materials in this blog are from a competitive reflective sheeting manufacturer