I just rolled a six-sided die a few times. I rolled: six, five, five, six, five. My question is: do you think the die is biased? One way to think about that question is to ask how likely I would be to roll only fives and sixes completely by chance. Not that likely: the odds are 242 to 1 against.

Before you conclude that I have crooked dice, let me mention something that had slipped my mind. As well as those fives and sixes, I also rolled four, three, three, three, two, two and one. But those results just didn’t seem that interesting, so I didn’t tell you about them. If that omission seems relevant, you’re beginning to appreciate the importance of the nerdy-sounding “trial register”.

Every day, across the world, researchers are conducting randomised controlled trials (RCTs). Some are rigorous, painstaking quests for truth, while others may cut a few corners in the search for a career-defining publication, or a licence for a new drug compound. But even if each individual trial was unimpeachable, the results would mean very little if there was a systematic bias in favour of a particular kind of result.