What research is there suggesting modal dialogs are disruptive?

Question

It seems "Everyone" knows they're highly disruptive for many situations but often times clients don't. Particularly in desktop applications this form of dialog is often misused, often disrupting a workflow.

I intellectually know all of the reasons to avoid them and some rare cases they may be warranted, and we have a great deal of anecdotal evidence and professional opinions in our modal-dialog questions.

I know there is published research on modal dialogs, but to my dismay few people reference this research when supporting or opposing the use of modals dialogs.

I know for example that distracting users while in a state of flow (such as writing an essay in Microsoft Word) can be easily destroyed by interruptions such as modal dialogs, having disastrous results on productivity.

In my particular case the issue is attention (working on the mistaken opinion that modal dialogs attract attention and comprehension) and productivity as the dialog disrupts workflow for a "confirmation".

What are the most convincing resources to give to a client who believes modal dialogs are not problematic?

I am particularly looking for scholarly articles, but high level explanations (which cite real data) may be applicable as well.

Wikipedia has a good list of "common knowledge" about and criticisms of modal windows, but even they mostly cite blog posts and a couple books.

Answer 1

Generally speaking, disruptions and distractions negatively affect human performance, a common finding in cognitive psychology. Many studies have shown that distraction greatly increases task time on a wide variety of tasks.

There also exist many Quantitative studies showing task performance is negatively affected by distractions (note these figures are not specifically for modal dialog distractions):

We can all relate to the above distractions, but what is their quantitative effect on our performance?
- Forgetting the as-left conditions: 45%
- Forgetting to return to the original task: 25%
- Original task out of control during distraction: 17%
- Not knowing changes after returning to original task: 13%

How does this relate to modal dialogs? Users find dialog windows distracting. The linked University of Minnesota study found users rated dialog windows to be considerably more distracting than two other tested window types.

Dialog windows in particular show an extreme effect on task performance (emphasis mine):

Results show that when peripheral tasks interrupt the execution of primary tasks, users require from 3% to 27% more time to complete the tasks, commit twice the number of errors across tasks, experience from 31% to 106% more annoyance, and experience twice the increase in anxiety than when those same peripheral tasks are presented at the boundary between primary tasks.

Subjects unanimously rated the dialog window as the most distracting (intrusive) awareness technique.

Other research has specifically found that interruptions from modal dialogs greatly increase error rates in a simple form workflow exercise.

On average, errors were made 7.14% (SD = 8.06%), 17.26% (SD = 7.28%) and 25.89% (SD = 9.88%) of the time in the zero-, one- and two-interruption conditions respectively

In addition, research on video games have shown that Calm Messaging improves task performance (pdf download link). Emphasis mine:

Games have shown that reducing demands on the user’s attention can aid performance; through the use of sound, speech, transient text, and animation, games communicate in a calm manner that promotes a fluid, uninterrupted workflow.

Bottom line: Modal dialogs can double error rates, increase time to task completion, and are near-universally despised by users. Alternate means of notification are often available and should be utilized wherever possible and appropriate.

Answer 2

I have found that some of the works by Mihaly Csikszentmihaly is a really good start. His understanding of flow is of critical importance. The point is that the flow of a task is critical, and dialogs - or anything else - that interrupts this flow is bad in terms of performance in completing this task. His classic book Flow is a good start.

Of course, if the most important thing is not the individuals performance in completing the task, then this is less relevant - there may be a higher priority of Not Corrupting the Corporate Database, and so interrupting the Flow state is a good thing.

So I think you need to make sure that you address the question of what is most important.

And when I have finished my PhD, you can refer to that. It might not be for a while yet, though :(

Answer 3

I would like to contribute by pointing to an extract of Apple's iOS UX guidelines:

People appreciate being able to accomplish a self-contained subtask in a modal view, because the context shift is clear and temporary.

Answer 4

Possibly related is this study looking at location-updating effect of doorways on context-memory

Gabriel A. Radvansky, Ph.D., from the University of Notre Dame in Indiana, and colleagues examined whether the location-updating effect of walking through a doorway reflects the influence of the experienced context, in terms of the degree of immersion of an individual in a specific environment, or in terms of a shift in context.

Three experiments were conducted using different environments.

• In the first, smaller displays were used to measure the degree of immersion on location-updating effects.
• In the second experiment, immersion was maximized using an actual, and not a virtual, environment.
• The third experiment examined whether the original encoding context was reinstated by returning to the original location where the objects were encoded

Answer 5

You can put numbers into an argument and over think it while the answer is very simple right in your face, literally as a modal dialog.

I go by a simple guidelines of using modal dialogs.

• If the application or web app cannot continue without the user's decision, use a modal dialog.
• If your application or web app has to have the user's decision immediately more than 5% of its interaction, rethink your application to support more "oops" user scenarios such as using trash and archiving as opposed to permanently deleting things that can never be recovered by a quick decision.
• User initiated modal dialogs do not count, meaning think of them as shortcuts or sub pages as they serve a purpose to quickly modify a small chunk of data. However, if it can be done inline effectively, inline wins over dialog.
• Use the checkbox "next time do not warn me about [blah blah]" if the modal could potentially annoy but must be told like Firefox does.

User studies are nice but its sometimes difficult to know what to look for in terms of the numbers. Asking someone do you like this or that isn't so useful on its own. It should be noted how people feel after they use your application or web app. Do they feel annoyed, happy at ease etc? What is your desired feeling? Try using the app yourself trying to actually use it for what it is trying to accomplish for the end user and take your head out of the implementation. Be the user. You will quickly see the annoyances. Try to eliminate them if you can by your design choices in your app. Numbers are good but common sense is way more valuable.