Michael Nicholls and his colleagues have drawn attention to another problem with relying on student participants - those who volunteer late in their university term or semester lack motivation and tend to perform worse than those who volunteer early.
A little background about student research participants. Psychology students often volunteer for numerous studies throughout a semester. Usually, they're compelled to do this at least once in return for course credits that count towards their degree. Other times they receive cash or other forms of compensation. When in the semester they opt to volunteer for course credit is usually down to their discretion. To over-generalise, conscientious students tend to volunteer early in semester, whereas less disciplined students leave it until last minute, when time is short and deadlines are pressing.
Nicholls team first recruited 40 students participants (18 men) at Flinders University during the third week of a 14-week semester. Half of them were first years who'd chosen to volunteer early in return for course credits. The other half of the participants, who hailed from various year groups, had chosen the option to receive $10 compensation. The challenge for both groups of students was the same - to perform 360 trials of a sustained attention task. Each trial they had to press a button as fast as possible if they saw any number between 1 and 9, except for the number 3, in which case they were to withhold responding.
At this early stage of the semester there was no difference in the performance (based on speed and accuracy) of the students who volunteered for course credit or for money. There was also no difference in their motivation levels, as revealed in a questionnaire.
Later in the semester, between weeks 9 to 12, the researchers repeated the exercise, with 20 more students who'd enrolled for course credit and 20 more who'd applied to participate in return for cash compensation. Now the researchers found a difference between the groups. Those participants receiving financial payment outperformed those who had volunteered in return for course credit. The latter group also showed more variability in their performance than their course-credit counterparts had done at the start of the semester, and they reported having lower motivation.
These results suggest that students who wait to volunteer for course credit until late in the semester lack motivation and their performance suffers as a result. Nicholls and his colleagues explained that their findings have serious implications for experimental design. "A lack of motivation and/or poorer performance may introduce noise into the data and obscure effects that may have been significant otherwise. Such effects become particularly problematic when experiments are conducted at different times of semester and the results are compared."
One possible solution for researchers planning to compare findings across experiments conducted at different ends of a semester, is to ensure that they only test paid participants. Unlike participants who are volunteering for course credit, those who are paid seem to have consistent performance and motivation across the semester.
Nicholls, M., Loveless, K., Thomas, N., Loetscher, T., & Churches, O. (2014). Some participants may be better than others: Sustained attention and motivation are higher early in semester The Quarterly Journal of Experimental Psychology, 1-19 DOI: 10.1080/17470218.2014.925481
The use and abuse of student participants
Improving the student participant experience
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.