Quick randomizing. Here’s a quick and easy way to randomize. You have 100 subjects, 50 women and 50 men. Toss a coin. If it’s heads, assign all the men to the treatment group and all the women to the control group. If the coin comes up tails, assign all the women to treatment and all the men to control.

This gives every individual subject a 50-50 chance of being assigned to treatment or control. Why isn’t this a good way to randomly assign subjects to treatment groups?