A colleague asked an interesting question, one that I am often asked as an evaluation specialist: “without a control group is it possible to show that the intervention had anything to do with a skill increase?” The answer to the question “Do I need a control group to do this evaluation?” is, “It all depends.”
It depends on what question are you asking. Are you testing a hypothesis–a question posed in a null form of no difference? Or answering an evaluative question–what difference was made? The methodology you use depends on what question you are asking. If you want to know how effective or efficient a program (aka intervention) is, you can determine that without a control group. Campbell and Stanley in their, now well read, 1963 volume, Experimental and quasi-experimental designs for research, talk about quasi-experimental designs that do not use a control group. Yes, there are threats to internal validity; yes, there are stronger designs; yes, the controls are not as rigorous as in a double-blind, cross-over design (considered the gold standard by some groups). We are talking here about evaluation, people, NOT research. We are not asking questions of efficacy (research); rather we want to know what difference is being made; we want to know the answer to “so what”. Remember, the root of evaluation is value; not cause.
This is certainly a quandary–how to determine cause for the desired outcome. John Mayne has recognized this quandary and has approached the question of attributing the outcome to the intervention in his use of contribution analysis. In community-based work, like what Extension does, attributing cause is difficult at best. Why–because there are factors which Extension cannot control and identifying a control group may not be ethical, appropriate, or feasible. Use something else that is ethical, appropriate, and feasible (see Campbell and Stanley).
Using a logic model to guide your work helps to defend your premise of “If I have these resources, then I can do these activities with these participants; if I do these activities with these participants, then I expect (because the literature says so–the research has already been done) that the participants will learn these things; do these things; change these conditions.” The likelihood of achieving world peace with your intervention is low at best; the likelihood of changing something (learning, practices, conditions) if you have a defensible model (road map) is high. Does that mean your program caused that change–probably not. Can you take credit for the change; most definitely.