Which statement best describes Kaufman's (2001) findings on the pattern of IQ change from young adulthood though old age generated by cross-sectional studies?

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Kaufman's (2001) findings suggest that IQ scores gradually increase until middle age (around 40-50), then slowly decline until old age (around 80). The decline then accelerates in very old age. This pattern of change was found in cross-sectional studies, which compare IQ scores from different age groups at the same time point. It should be noted that longitudinal studies, which follow the same individuals over time, show more variability in the pattern of IQ change across individuals.

Which Statement Best Describes Kaufman's (2001) Findings on the Pattern