My Most Important Scientific Contribution

I would consider the Seattle Longitudinal Study (SLS) to be my most important scientific contribution. This study has addressed the following questions:

1. 1. Do cognitive abilities age at the same rate across people?

2. 2. Do they decline at the same rate, starting when?

3. 3. How can these topics best be studied?

This research began as a cross-sectional study, in which different groups of adults between twenty and seventy years of age were studied at the same time. The goal was to determine the impact of rigidity-flexibility on age differences in Thurstone's Primary Mental Abilities. This sample was then retested every seven years until 2012, with new samples added at each test occasions. We also converted the study of age comparisons to a long-term study of age changes in the same individuals. Data collections were added to study personality traits, family characteristics, health behaviors, and social-environmental variables, as well as records of health problems. The brains of some study participants were also studied by means of MRI scans over a ten-year period.

In addition, we have conducted family studies of the children, siblings, and grandchildren of our original study participants. Cognitive training studies were also conducted over a twenty-one-year period to determine whether it was possible to increase the cognitive performance of people over sixty years of age to the performance level of individuals who had been tested fourteen years earlier, as well as whether it was possible to increase performance of older persons by means of training interventions.

Why Is It My Most Important Scientific Contribution?

1. 1. The study showed conclusively that cross-sectional data on age differences in cognitive performance cannot be used as an estimate of longitudinal change within individuals over their life span. This is because cross-sectional data compare different people, while change over time and age always involves the same individuals.

2. 2. We found vast individual differences in the rate of intellectual aging. People's thinking processes are differentially based on their educational attainment, occupational complexity, socioeconomic status, ability level of spouse, engagement in social and intellectual pursuits, and levels of cognitive flexibility.