LSAT Strengthen Practice Question: Random Assignment
An original strengthen question from our free Question of the Day rotation, built around a trap the LSAT reuses constantly: random assignment. Try it first, then read the explanation — it teaches the move, not just the answer.
Your job:Make the conclusion more believable.
Members of the Grelling Bay winter swim club report catching fewer colds each winter than their neighbors do. Club officers say this shows that regular cold-water swimming strengthens the immune system.
Which one of the following, if true, adds the most support to the officers' conclusion?
Show the answer & full explanation
The correct answer is D
The JBDM line
Just because swimmers catch fewer colds doesn't mean the swimming is why — maybe the healthy join, rather than the joining making them healthy.
The maybes
- MaybeMaybe robust people self-select into winter swimming.
- MaybeMaybe club members share other habits — exercise, time outdoors — that fight colds.
Why D is right
Random assignment is the whole game. When volunteers are assigned to cold water by coin flip, 'healthy people choose to swim' can't explain the difference — the groups start out alike. The cold water itself is the only systematic difference left, which is exactly what the officers claim.
Why the others are wrong
- AMild winters describe the setting; they don't connect swimming to immunity.
- BA few physician members adds a whiff of authority, not evidence.
- CThis is the self-selection problem stated outright — it weakens the argument.
- ECenturies of tradition prove popularity, not immune benefits.
Sammy's note
Random assignment is the chainsaw of strengtheners: it cuts the self-selection maybe off at the trunk.
What's a JBDM line?
Just Because Doesn't Mean (JBDM) is the Burton Method's foundational framework for attacking LSAT arguments: identify the premise, identify the conclusion, then say "just because [premise] doesn't mean [conclusion]" and generate "maybes" — alternative explanations that expose the gap between them. That gap is what weaken, flaw, strengthen, and assumption questions all test, so every explanation on this page starts with the JBDM line. It's a micro-lesson in the system, not just an answer key.
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Answer today's question and start a streak — then see how Sammy teaches the whole system, JBDM included, in a free lesson.