Surveys are commonly used as tools to measure the effect of treatments on patients’ quality of life and symptoms. However, surveys may introduce what are called ceiling or floor effects to a research study’s results if they aren’t properly designed for the patient population being studied. 

Let’s take pain in ME/CFS as an example. A survey not designed for the ME/CFS population might not have enough range in what it captures to really represent the patient experience. At baseline for a study, the majority of the patients might score at the very top of the pain scale, for example. Then, even if the intervention that’s tried does help some with pain, it’s possible they may still score at the very top and the study would completely miss the effect. That would be an example of a ceiling effect. You can imagine the opposite is true for a floor effect; that might come into play for something like a quality of life survey.

One survey that was designed for the ME/CFS population is the functional capacity questionnaire (FUNCAP). It incorporates a range of answers that accommodates even severe patients. Based on the design of the survey and its validation, Open Medicine Foundation is using the FUNCAP survey as a primary outcome measure in our clinical trial.