Passage Summary: Scientists found a link between a specific chromosome problem and schizophrenia, but the author claims it can't be a cause because the link isn't perfect—not everyone with the problem gets sick, and some sick people don't have the problem.

Conclusion: There is no causal link between damage to chromosome number six and adult schizophrenia.

Reasoning: The author points out that some people with the damage do not have the condition, and some people with the condition do not have the damage.

Analysis: The author is making a classic LSAT error by assuming that a cause must be both necessary and sufficient. Just because a factor doesn't always produce an effect, or isn't the only way to produce it, doesn't mean it isn't a cause. In the real world, many causes are 'contributing factors' rather than absolute triggers. Look for an answer that describes this failure to distinguish between a factor that is always present and a factor that simply increases the likelihood of an outcome.