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Instructional Manipulation Check (IMC)

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This task shows how to use an instructional manipulation check (IMC), which identifies participants who are not reading the study materials closely. The IMC is based on the IMC used in Oppenheimer, Meyvis, & Davidenko, 2009.

There are two versions of the IMC, omdimc1 and omdimc2. These files require no modification.

When you design a study, you can add an IMC by simply adding one of the following lines to your experiment (expt) file:

<Task id="omdimc">/common/en-us/html/omdimc1.jsp</Task>   

<Task id="omdimc">/common/en-us/html/omdimc2.jsp</Task>   

When should I use an IMC?

If your task requires a high level of focus from your participants.

How are the variables coded in the data?


JSP Variable Name Value when Passed Value when Failed
omdimc1.jsp omdimc1 . -900
omdimc2.jsp omdimc2 . 1


The difference between omdimc1 and omdimc2:

  • omdimc1 was the task used in the original Oppenheimer et al. 2009 paper. It includes a paragraph which instructs participants to click the “Welcome” above instead of answering the question below about what sports they participate in)
  • omdimc2 is an adapted version (without the questions about sports) that takes less time to complete and is less deliberatively deceptive. We have not found differences between omdimc1 and omdimc2, and we (PI) typically use omdimc2 since it is shorter.

For an alternative to the IMC that asks questions relevant to the current task, see: