The Data-Ink Ratio
In the last several posts, we’ve been considering the two major high-level user interface designs for organizing a patient’s EHR record over time – the Snapshot-in-Time Design that formed the core of much paper-based charting and the Overview-by-Category Design that has been much more widely adopted by EHR vendors.
Despite the widespread adoption of the Overview-by-Category design, it does a poor job of helping the physician understand the patient’s record as a narrative that unfolds over time. As a result, most EHRs employing the Overview-by-Category design also provide a workaround that does, in fact, provide the physician with a snapshot-in-time view – The Text-Based Workaround.
In my last post, we saw a major problem with the text-based chart notes generated by most EHRs – they have an exceedingly low data density. In addition, they often have a second problem –a low data-ink ratio.
The concept of the data-ink ratio was introduced in 1982 by Edward Tufte, a pioneer in the field of data visualization – the field of how to present abstract information graphically in formats optimized to take advantage of our high-bandwidth visual processing system.
Tufte defined the data-ink ratio as the amount of ink used to display data divided by the total amount of ink used in the graphic or display. He proposed that, within reason, good visual designs maximize the data-ink ratio, both by devoting a large share of the graphic to actual data and by pruning unnecessary and redundant non-data. Think of the data-ink ratio as the signal-to-noise ratio for graphics.
Let’s return to the same EHR-generated text-based chart note we’ve been considering and investigate how well it maximizes the data-ink ratio. The mockups shown below are a composite design based on several widely used EHRs.
Rick Weinhaus, MD practices clinical ophthalmology in the Boston area. He trained at Harvard Medical School, The Massachusetts Eye and Ear Infirmary, and the Neuroscience Unit of the Schepens Eye Research Institute. He writes on how to design simple, powerful, elegant user interfaces for electronic health records (EHRs) by applying our understanding of human perception and cognition. He welcomes your comments and thoughts on this post and on EHR usability issues. E-mail Dr. Rick.