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Choosing the right participants for your study

This is an excerpt from Research Methods in Physical Activity-7th Edition by Jerry Thomas,Jack Nelson & Stephen Silverman.

Describing Participants


This section of the method of a thesis or dissertation describes how and why the participants were selected and which of their characteristics are pertinent to the study. These are questions to consider when selecting participants:

  • Are participants with special characteristics necessary for your research?
    • Age (children, elderly)
    • Sex (females, males, or both)
    • Level of training (trained or untrained)
    • Level of performance (experts or novices)
    • Size (weight, fatness)
    • Special types (athletes, cyclists, runners)
  • Can you obtain the necessary permission and cooperation from the participants?
  • Can you find enough participants?

Of course, you want to select participants who will respond to the treatments and measures used in the study. For example, if you want to see the results of training a group of children in overhand throwing, selecting expert 12-year-old baseball pitchers as participants will not likely produce a change in measures of throwing outcome. An intense, long-term training program would be required to have any influence on these participants. Selecting children who are soccer players and have never played organized baseball would offer better odds for a training program to produce changes.


In experimental research, the interactions among participants, measures, and the nature of the treatment program are essential in allowing the treatment program to have a chance to work (Thomas, Lochbaum, Landers, & He, 1997). If you select participants who have high levels of physical fitness, subjecting them to a moderate training program will not produce changes in fitness. Also, participants high in physical fitness will have a small range of scores on a measure of cardiorespiratory endurance (e.g., V over timeO2max). For example, you will not find a significant correlation between V over timeO2max and marathon performance in world-class marathon runners. Their range of scores in V over timeO2max is small, as is their range of scores in marathon performance times. Because the range of scores is small in both measures, no significant correlation will be found. This result does not mean that running performance and cardiorespiratory endurance are not related. It means that you have restricted the range of participants’ performance so much that the correlation cannot be exhibited. If you had selected moderately trained runners (e.g., women who jog three times per week for 40 min each time), a significant correlation would be found between running performance on a 5K run and V over timeO2max. (We discuss procedures for selecting sample participants in chapter 6.)


Participants, measures, and treatment programs are interrelated. Be sure to choose participants who will respond to the treatment program and have a broad enough range of results when measured with the chosen techniques.


You may have to offer something to the participants to make being in the study worthwhile.
You may have to offer something to the participants to make being in the study worthwhile.


What to Tell About the Participants

The exact number of participants should be given, as should any loss of participants during the time of study. In the proposal, some of this information may not be exact. For example, the following might describe the potential participants:


Participants: For this study, 48 males, ranging in age from 21 to 34 years, will be randomly selected from a group (N = 147) of well-trained distance runners (V over timeO2max = 60 ml · kg · min - 1 or higher) who have been competitive runners for at least 2 years. Participants will be randomly assigned to one of four groups (n = 12).


After the study is completed, details are available on the participants, so now this section might read as follows:

Participants: In this study, 48 males, ranging in age from 21 to 34 years, were randomly selected from a group (N = 147) of well-trained runners (V over timeO2max = 60 ml · kg · min - 1 or higher) who had been competitive runners for at least 2 years. The participants had the following characteristics (standard deviations in parentheses): age, M = 26 years (3.3); height, M = 172.5 cm (7.5); weight, M = 66.9 kg (8.7); and V over timeO2max, M = 65 ml · kg · min - 1 (4.2). Participants were randomly assigned to one of four groups (n = 12).


The participant characteristics listed are extremely pertinent in an exercise physiology study but not at all pertinent, for example, in a study of equipment used by children on the playground. The nature of the research dictates the participant characteristics of interest to the researcher. Carefully think through the characteristics that you will report in your research. Look at related studies for ideas about important characteristics to report.


The characteristics of participants that you identify and report must be clearly specified. Note in the example that well-trained runners were exactly defined; that is, their V over timeO2max must be equal to 60 ml · kg · min - 1 or higher. When participants of different ages are to be used is another good example. Saying only that 7-, 9-, and 11-year-olds will be the participants is not sufficient. How wide is the age range for 7-year-olds? Is it ±1 month, ±6 months, or what? In the proposal, you may say that 7-, 9-, and 11-year-olds will be included in the study. At the time of testing, each age will be limited to a range of ±6 months. Then, when the thesis or dissertation is written, it may read as follows:

At each age level, 15 children were selected for this study. The mean ages are as follows (standard deviations in parentheses): the youngest group, 7.1 years (4.4 months); 9-year-olds, 9.2 years (3.9 months); and the oldest group, 11.2 years (4.1 months).

A graduate student we know was in his committee meeting when a faculty member on his committee asked him to describe one of his participants. The student said, "Hewas 6 feet tall, had brown hair and a beard, and trained regularly by distance running." The really sharp faculty member then asked, "Was this a male or female?" to which the student was unable to respond because of laughter.

Learn more about Research Methods in Physical Activity.