Did the messages make the difference?
Twenty-eight people, picked at random as they came in, got no WhatsApp messages. The front desk called them back the way it always had. Setting the two side by side is the fair way to see what the messages add on their own.
People who got the messages booked more often: about 18 in every 100, against about 11 for the front desk alone. But only 28 people were left to the front desk, and with so few, a gap like this turns up about one time in three by chance, even when the messages change nothing.
Telling a gap this size apart from chance takes roughly 390 people in each group. Until then the comparison keeps running, and each Monday the card says plainly whether it can tell yet.
Sample card. Every count on it comes from a made-up contact list. A real card also shows how fast each person got a reply and who did not turn up; those are left off here because this sample has no measured figures for them.