Organising a sports session between strangers without anyone dropping out

You booked the court, you found five people, and the night before there are two left. It is the most ordinary problem in organising sport, and also the least documented. Here is what research actually establishes, what it does not, and what you can do with it.

Do we know how many people drop out of a sports session?

No, and that has to be said up front. No public French source measures the drop-out rate on a sports booking. Neither the federations nor the booking platforms publish it. Every percentage in circulation comes from another field, usually healthcare or restaurants.

What does exist is a solid body of work on what makes people turn up to an appointment. It was built elsewhere, but its mechanisms transfer, as long as nobody passes off a medical figure as a sporting one.

Does a reminder before the session change anything?

Yes, but less than you would think. The 2013 Cochrane review on text message reminders, pooling eight randomised trials and 6 615 participants, measures an attendance rate of 67,8 % without a reminder against 78,6 % with one. The strength of evidence is rated moderate. Put another way, a reminder prevents about a third of absences, not all of them.

The content of the message matters more than the message itself. Two British randomised trials published in PLOS ONE in 2015, each covering around ten thousand people, show that a message stating the precise cost of a missed appointment cuts absenteeism from 11,1 % to 8,4 %. The vague version of the same message does clearly worse than the costed one. That is healthcare, not sport, but the lesson is plain: saying what an absence costs works better than repeating the time.

Does taking payment upfront solve it?

Prepayment helps, but the effect is weaker and more fragile than the folklore suggests. The only randomised trial that directly compares a deposit with a reward, published in 2022 on 126 young adults, finds no significant difference between the two. More importantly, only 62 % of participants accept the deposit, against 100 % for the reward.

In other words, a deposit holds on to waverers, but it also drives some of them away before they even sign up. It selects as much as it retains, and existing data cannot separate the two effects. Nobody can therefore claim that prepayment halves drop-outs.

One result still deserves attention. A study of about a thousand employees at a large company shows that once a financial incentive stops, roughly 16 % of the effect remains, against roughly 47 % among those who had been able to sign a self-funded commitment. Voluntary commitment holds better than the carrot, but only 12 % accepted it.

Why do strangers drop out more than friends?

Because it has been measured. The reference meta-analysis on social loafing, published in 1993 across 78 studies, finds a clear average effect, but its moderating variables are the interesting part. Among close friends the effect reverses: people do more than expected. Among strangers it is plainly present.

The second lesson is the most actionable: when each person’s contribution stays identifiable, the effect almost entirely collapses. A named place, an assigned role, a message where everyone confirms in front of the others is not politeness. It makes visible what anonymity erases.

How many people should you aim for?

No study gives an optimal group size for a sports session. The literature establishes a positive correlation between group size and social loafing, without ever setting a threshold. The numbers you read everywhere rest on no measurement in a sporting context.

What is documented is that practising with others goes together with better attendance, and that a group built on real principles of collective dynamics does better than a plain class. Careful though, these are associations and not proof of causation: people who train in groups may simply be the ones who were already the most motivated.

What should you actually do for your next session?

Five moves, all consistent with the above. Announce the real cost of the slot and what an absence puts on the others, rather than repeating the time. Assign named places so that everyone’s presence is visible to the group. Plan one place more than the strict minimum, so the session survives a drop-out.

Then offer prepayment without forcing it if you are just starting, since it turns some candidates away. And above all, keep the same slot every week with the same people, because the only mechanism that durably reverses the trend is that strangers stop being strangers.