Passage Summary: A study found that older people say they give blood more often than younger people, so researchers called them more selfless. However, the author points out that people often just say what they think sounds good to others.

Conclusion: The conclusion that fifty-year-olds are more altruistic than twenty-year-olds is based on questionable evidence.

Reasoning: The study relies on self-reporting, and people often lie about their behavior to appear more socially acceptable.

Analysis: The author is attacking the 'internal validity' of the study by suggesting a bias in the data collection method. Specifically, the argument points out that 'reported behavior' is not the same as 'actual behavior.' In the world of social science, this is known as social desirability bias. The author isn't saying fifty-year-olds *aren't* more altruistic; they are simply saying the survey doesn't prove it because the respondents might be exaggerating their virtues to look better to the researchers.