MailerMailer – Improving Subscriber Experience: Fitts’ and Hick’s Laws as Applied to Email Design
Positive subscriber interaction relies not only on quality content, but on structuring that content in a way that streamlines the subscriber’s decision-making process. Fitts’ Law and Hick’s Law have become staples in the field of human-computer interaction for setting design guidelines that enhance usability, and in turn, user experience. These laws are commonly used to justify the size, orientation, and number of interactive objects on websites. But, what do Fitts’ and Hick’s Laws tell us about email design?
In 1954, Paul Fitts published an article that detailed his theory on human mechanics as it pertained to aimed movement. With Fitts’ Law, the action of pointing to or tapping a target object can be measured and predicted mathematically. More specifically, the time required to move to a target is a function of the target size and distance to the target. Mathematically, this can be expressed as:
In other words, time (T) is a function of distance (D) and width (W), where a and b are empirically determined regression coefficients– they build the slope between the starting point and target.
Pointing movements, like moving a mouse over a link and clicking it typically begin with a quick movement toward the target (ballistic movement) followed by fine-tuning movements (homing movements) over the target. Homing movements take the most time and are responsible for the majority of errors.
Bigger and closer targets will generally be acquired more quickly. However, since the relationship is logarithmic and not simply linear, Fitts’ law will have diminishing returns at certain points. For instance, a very small object will become significantly easier to click given a 20% size increase than a very large object given that same increase.
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