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Modulo can skew random selection when the choice count does not divide the range

ersc.io 8 min read Editor score 7/10

Taking a random integer modulo the number of choices does not preserve a uniform distribution when the range is not evenly divisible. Engineers writing sampling or selection code should account for this bias rather than assume each outcome is equally likely.

What

Using modulo to map a uniformly random number to a choice count can make some choices more likely than others.

How

With 10 equally likely inputs mapped to 3 choices, modulo gives one choice 40% probability and the other two 30% each.

Why it matters

Engineers implementing random selection need to account for distribution bias; the excerpt recommends a `random_between` function for uniform ranges.

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