How Many Participants Do I Need For My Research Study?

You have a hypothesis, and your research study is ready to go—now how many participants are enough to test your theory? Research Statistics provide a good estimate for the numbers of people you need to test, but what about the actual number you need to finish that requirement? In other words, if you need 50 people to complete your study, you may have to recruit 100 (or more!) to start.

There are many reasons why participants register for a study and then decide not to call you back, or fail to show up to their scheduled appointment, or disappear after having completed the first part of the study. There are many other reasons why out of a confirmed 100 participants, only 50 may ever get to the finish line of your study. And those 50 may get there in one year instead of the 6 months you set aside for it. This is known as participant attrition or participant delay and is often not accounted for in the research timeline.

The Wall Street Journal found that time and time again researchers underestimate the number of participants that they will need for a successful study completion. For example, “about 40% of clinical trials don’t recruit enough patients to meet their goals.”

Participant attrition rates will vary based on several factors:

  1. Length between initial participant sign-up for a study and the researcher’s confirmation/scheduling of the participant. The longer the interval, the less likely a participant will respond to a researcher’s call or remember what they signed up for. Interest wanes quickly.
  2. Number of appointments a participant must attend to complete the study. Researchers have found that, on each consecutive lab/study visit, they lose an average of 11% or more of their participants. Repeat visits must be incentivized carefully, scheduled in advance, and appointment reminders need to be sent often.
  3. Amount of money paid to participants for showing up. As a general rule, the less reimbursement a participant receives, the less likely they are to show up.
  4. How you incentivize study attendance after participant registration. Participants who will have repeat interactions with the researcher, or don’t receive some third party credit (e.g., graduation credits for psych 101 students) are less likely to show up.

Additionally, participants may show up, but do so on a delayed timeframe and reschedule their appointments frequently, extending the length of time needed to complete the study.

Therefore, as you plan your study and its recruitment, think carefully about the number of participants you’ll need, the length of time that they will be recruited, and a detailed plan of participant incentives and timelines to minimize participant attrition.


Research And Me provides several ways to minimize participant attrition by allowing Researchers to advertise, manage, and communicate with participants online and have frequent interaction, without having to pay more for participant compensation. This reduces the amount of time, money and attrition spent on participant recruitment.

Join Research And Me to jump start your research participant recruitment today and use the Promo Code BLOG2016 to receive 50% off your first study listing!

How Many Participants Do I Need For My Research Study?
Tagged on:                                                                 

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.