NA TIG Week: Necessity and Sufficiency Relationships by Ryan Watkins

Underlying any needs assessments is a concept of what is a “need.”  I’m Ryan Watkins and I teach how to do needs assessments at George Washington University and for The Evaluator’s Institute. It can be implied from the word that a need refers to a relationship where something is “needed,” or in other words that there is a necessity relationship.  In needs assessments we begin by looking for those necessity relationships as they link together results – result X is necessary to achieve result Y.

We then tie several of those relationships together as the basis for a Theory of Change.  For example, a community organization may determine that a delivered service or output (X) is necessary to achieve an outcome (Y) for their clients.  Further, the clients must achieve the outcome (Y) in order for the community to accomplish a desired impact (Z).

Necessity relationships are tricky however; necessity leaves little wiggle room. If you state that X is necessary for Y, then you are saying that there is no way to accomplish Y without having achieved X. Often these relationships appear clear; but rarely are they. Whereas initially we may believe that, in order to achieve a desired cholesterol level (Y) we have to maintain adherence to a prescription medication (X1); we may now learn that maintaining a healthy lifestyle (X2) is also necessary – yet neither may be sufficient. Today X3 is necessary, tomorrow it is not.  Necessity relationships can get complex.

However, we get into necessity troubles when we try to extend these necessity relationships to what we may do in order to achieve those results.  Here is why: system theory posits (in the principle of equifinality) that in open systems there are always alternatives for achieving any result. The options may not be desirable, but they do exist. These options, however, keep us from being able to claim necessity in the relationship between an activity (which the literature often refers to as solutions or satisfiers) and a result.  That is, an activity (A) can’t be necessary to achieve result (X) since there are always options to consider.  Activity A may be the most desirable activity for achieving X, but that is different than saying it is necessary. Likewise, A may be sufficient for achieving X, but still not be necessary.

Hot Tip:  Clarity in language can improve decisions.

With sufficient evidence, we state that one result is necessary for the achievement of another result – and we call these needs. But we can’t say that any activity or intervention is necessary to achieve those results, we must note that there are always alternatives. Fortunately, just knowing that there are options can lead us to better decisions.

Rad Resources:

Using set theory, Qualitative Comparative Analysis (QCA) techniques give us tools for measuring necessity relationships. The open-source statistics platform, R, now has a free QCA package you can install to analyze case study data.

Concept map of Principle of Equifinality


The American Evaluation Association is celebrating Needs Assessment (NA) TIG Week with our colleagues in the Needs Assessment Topical Interest Group. The contributions all this week to aea365 come from our NA TIG members. Do you have questions, concerns, kudos, or content to extend this aea365 contribution? Please add them in the comments section for this post on the aea365 webpage so that we may enrich our community of practice. Would you like to submit an aea365 Tip? Please send a note of interest to aea365 is sponsored by the American Evaluation Association and provides a Tip-a-Day by and for evaluators.

3 thoughts on “NA TIG Week: Necessity and Sufficiency Relationships by Ryan Watkins”

  1. I appreciate the outlook on this, as people tend to chalk fixing something down to one specific solutions instead of looking and taking into consideration any other alternatives. If no other alternatives are tested, we may never know if they will have an effect on the perceived need. The way you explained the necessity relationships is spot on, because they are at a high complexity level. With them being so complex it tends to run people away, so keeping an alternative route will prepare for the most improvements. The diagram is very resourceful, and thank you for this informative blog. You have provided great insight and it was very helpful!

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