From 7 field tests; effect inverts above ~7 options, where the dropdown's compactness wins.
Radios are single-tap and fully visible — no hidden second interaction. But past ~7 choices they overwhelm the viewport and scrolling cost overtakes the tap savings.
— ≤5 options: radio ▮▮▮▮▮▮ vs dropdown ▮▮▮▮
— >7 options: dropdown ▮▮▮▮▮▮ vs radio ▮▮▮
Match the control to the option count, not to a global style rule.
Read the number, not the story. [n=7 tests · count-dependent]
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Replacing a dropdown with radio buttons lifts completion ~1.8% when options number ≤5.
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