Three different customers recently asked me how to decide between scoring a multiple-response (MR) item dichotomously or polytomously; i.e., when should an MR item be scored right/wrong, and when should we give partial credit? I gave some garrulous, rambling answers, so the challenge today is for me to explain this in a single blog post that I can share the next time it comes up.
In their chapter on multiple-choice and matching exercises in Educational Assessment of Students (5th ed.), Anthony Nitko and Susan Brookhart explain that matching items (which we may extend to include MR item formats, drag-and-drop formats, survey-matrix formats, etc.) are often a collection of single-response multiple choice (MC) items. The advantage of the MR format is that is saves space and you can leverage dependencies in the questions (e.g., relationships between responses) that might be redundant if broken into separate MC items.
Given that an MR items is often a set of individually scored MC items, then a polytomously scored format almost always makes sense. From an interpretation standpoint, there are a couple of advantages for you as a test developer or instructor. First, you can differentiate between participants who know some of the answers and those who know none of the answers. This can improve the item discrimination. Second, you have more flexibility in how you choose to score and interpret the responses. In the drag-and-drop example below (a special form of an MR item), the participant has all of the dates wrong; however, the instructor may still be interested in knowing that the participant knows the correct order of events for the Stamp Act, the Townshend Act, and the Boston Massacre.
Are there exceptions? You know there are. This is why it is important to have a test blueprint document, which can help clarify which item formats to use and how they should be evaluated. Consider the following two variations of a learning objective on a hypothetical CPR test blueprint:
- The participant can recall the actions that must be taken for an unresponsive victim requiring CPR.
- The participant can recall all three actions that must be taken for an unresponsive victim requiring CPR.
The second example is likely the one that the test developer would use for the test blueprint. Why? Because someone who knows two of the three actions is not going to cut it. This is a rare all-or-nothing scenario where knowing some of the answers is essentially the same (from a qualifications standpoint) as knowing none of the answers. The language in this learning objective (“recall all three actions”) is an indicator to the test developer that if they use an MR item to assess this learning objective, they should score it dichotomously (no partial credit). The example below shows how one might design an item for this hypothetical learning objective with Questionmark’s authoring tools:
To summarize, a test blueprint document is the best way to decide if an MR item (or variant) should be scored dichotomously or polytomously. If you do not have a test blueprint, think critically about what you are trying to measure and the interpretations you want reflected in the item score. Partial-credit scoring is desirable in most use cases, though there are occasional scenarios where an all-or-nothing scoring approach is needed—in which case the item can be scored strictly right/wrong. Finally, do not forget that you can score MR items differently within an assessment. Some MR items can be scored polytomously and others can be scored dichotomously on the same test, though it may be beneficial to notify participants when scoring rules differ for items that use the same format.
If you are interested in understanding and applying some basic principles of item development and enhancing the quality of your results, download the free white paper written by Austin: Managing Item Development for Large-Scale Assessment