Participants are contributing to research and, in some cases, volunteer a substantial amount of time.
A feedback letter or letter of appreciation is one method that researchers can use to express appreciation and possibly provide further information on the study and preliminary findings. "Researchers, including student researchers, have an ethical responsibility to make reasonable efforts to publicly disseminate research findings in appropriate venues, in a timely manner and without undue restriction" (TCPS 2, Article 4.8).
Samples
General feedback letter (Word)
Online survey appreciation/closing page (Word)