Kern, Jill P. (1987, ASQC) Digital Equipment Corp., Stow, MA
Do you ever get fooled by the way data is presented in a graph? Has a graph ever given you an incorrect message, and unclear message, or even no message at all?You are not alone!And, when designing your own graphs, you should be aware of ways to avoid these problems, so you can create clear, understandable, and even interesting displays of data to get your true message across.This session will cover some of the human perception constraints which apply to graphing of data. I will display and discuss a number of successful and unsuccessful graphs based on knowledge of perception constraints.Both the human eye and the human mind play roles in the perception of graphical data displays. For example, the human eye can only differentiate between closely-spaced marks on a page to a certain point, and large differences along a visual dimension are noticed before subtle ones. In addition, there are some systematic distortions in perception (such as the eye's ability to detect ratios, angles and areas) that need to be recognized and compensated for.The brain, and in particular memory, also apply constraints to graphing. Short-term memory capacity is roughly four perceptual units. Many graphs violate this constraint by presenting too much material, or having a long key or legend that must be memorized in order to understand the display. Long-term memory is also accessed when the audience must link graphed data patterns with what they know about the meaning of such aptterns. The correct pattern must be presented to match their knowledge or the connection may be missed.Many problems with graphs can be minimized or avoided by increasing your awareness of our perceptual limitations and biases. In addition, employing some creativity (and even a touch of irreverence) in developing graphs can yield displays that are interesting and fun to interpret. This increases the likelihood that your message will be received and remembered.
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