collider bias can so easily trap the unwary. In the two-coin experiment, the choice was conscious: I told you not to record the trials with two tails. But on plenty of occasions we aren’t aware of making the choice, or the choice is made for us. In the Monty Hall paradox, the host opens the door for us. In Berkson’s paradox, an unwary researcher might choose to study hospitalized patients for reasons of convenience, without realizing that he is biasing his study.
