Crowdsourcing User Studies for Formal Methods

Tags: Verification, User Studies

Posted on 03 July 2017.

For decades, we have neglected performing serious user studies of formal-methods tools. This is now starting to change. An earlier post introduces our new work in this area.

That study works with students in an upper-level class, who are a fairly good proxy for some developers (and are anyway an audience we have good access to). Unfortunately, student populations are problematic for several reasons:

  • There are only so many students in a class. There may not be enough to obtain statistical strength, especially on designs that require A/B testing and the like.

  • The class is offered only so often. It may take a whole year between studies. (This is a common problem in computing education research.)

  • As students progress through a class, it’s hard to “rewind” them and study their responses at an earlier stage in their learning.

And so on. It would be helpful if we could obtain large numbers of users quickly, relatively cheaply, and repeatedly.

This naturally suggests crowdsourcing. Unfortunately, the tasks we are examining involve using tools based on formal logic, not identifying birds or picking Web site colors (or solving CAPTCHAs…). That would seem to greatly limit the utility of crowd-workers on popular sites like Mechanical Turk.

In reality, this depends on how the problem is phrased. If we view it as “Can we find lots of Turkers with knowledge of Promela (or Alloy or …)?”, the answer is pretty negative. If, however, we can rework the problems somewhat so the question is “Can we get people to work on a puzzle?”, we can find many, many more workers. That is, sometimes the problem is one of vocabulary (and in particular, the use of specific formal methods languages) than of raw ability.

Concretely, we have taken the following steps:

  • Adapt problems from being questions about Alloy specifications to being phrased as logic “puzzles”.

  • Provide an initial training phase to make sure workers understand what we’re after.

  • Follow that with an evaluation phase to ensure that they “got the idea”. Only consider responses from those workers who score at a high enough threshold on evaluation.

  • Only then conduct the actual study.

Observe that even if we don’t want to trust the final results obtained from crowdsourcing, there are still uses for this process. Designing a good study requires several rounds of prototyping: even simple wording choices can have huge and unforeseen (negative) consequences. The more rounds we get to test a study, the better it will come out. Therefore, the crowd is useful at least to prototype and refine a study before unleashing it on a more qualified, harder-to-find audience — a group that, almost by definition, you do not want to waste on a first-round study prototype.

For more information, see our paper. We find fairly useful results using workers on Mechanical Turk. In many cases the findings there correspond with those we found with class students.