External Validity in Impact Evaluation: Overview, Importance, and Ways to Improve

One of the key questions, which comprises the soul of impact evaluation, is the attribution question to ascertain a specific intervention’s treatment effect. One must establish whether or not one received outcomes and whether or not those outcomes were the product of actions, conditions, or other intervention variables. To arrive at a credible response, it is necessary to determine if the observed outcomes were caused by the intervention or by other causes. It’s easier said than done, and the most important roadblock in attribution is the key construct of threat to internal and external validity.  

Internal and external validity indicates whether the results of an evaluation are credible and relevant. The researcher must limit any threats to any evaluation study’s internal and external validity.  

Threats to external validity 

These affect your ability to use the results of your study in other situations. They make it more likely that your program and its results can be used elsewhere or with others. Concerns about external validity (or generalizability) can arise when other variables interact with the program or intervention or when the program is set up in a certain way.  

Let’s look at a few of the things that can hurt external validity

Sampling Bias: A sampling bias occurs when units from the target population aren’t chosen correctly, so the sample doesn’t represent the population as a whole. It makes it harder to apply the sample to the whole population, lowering its external validity. 

Treatment Interaction: This refers to the idea that different treatments work better or worse for different people because of their unique abilities. It is a rule of thumb that each learner needs to be taught in a way that fits their level of knowledge. 

Situation Effect: The situation effect comprises the different situations that can make a study’s results less reliable. It includes the time of day, location, researcher’s personality, setting, and more. These things could make it hard for the research results to be used in other situations. 

To improve the external validity of an experiment, you can use the following three tips: 

Choose the Right Sampling Method: Carefully consider which method will work best for your study. You have to choose one that lets you get a sample group representing the study’s larger group. 

Replicating the Study: Doing your study more than once can help ensure that your research results can be applied to other periods, environments, and populations. 

Do field experiments: Field experiments are tests done in the real world, not in a lab. Field experiments have more external validity than studies done in controlled environments because they are more generalizable and take place in the real world. 

Kultar Singh – Chief Executive Officer, Sambodhi