Longitudinal study of performance on the Ruff Figural Fluency Test in persons aged 35 years or older.

The Ruff Figural Fluency Test (RFFT) is a cognitive test to measure executive function. Longitudinal studies have shown that repeated testing improves performance on the RFFT. Such a practice effect may hinder the interpretation of test results in a clinical setting. Therefore, we investigated the longitudinal performance on the RFFT in persons aged 35-82 years. Performance on the RFFT was measured three times over an average follow-up period of six years in 2,515 participants of the Prevention of REnal and Vascular ENd-stage Disease (PREVEND) study in Groningen, the Netherlands: 53% men; mean age (SD), 53 (10) years. The effect of consecutive measurements on performance on the RFFT was investigated with linear multilevel regression models that also included age, gender, educational level and the interaction term consecutive measurement number x age as independent variables. It was found that the mean (SD) number of unique designs on the RFFT increased from 73 (26) at the first measurement to 79 (27) at the second measurement and to 83 (26) at the third measurement (p<0.001). However, the increase per consecutive measurement number was negatively associated with age and decreased with 0.23 per one-year increment of age (p<0.001). The increase per consecutive measurement number was not dependent on educational level. Similar results were found for the median (IQR) number of perseverative errors which showed a small but statistically significant increase with repeating testing: 7 (3-13) at the first measurement, 7 (4-14) at the second measurement and 8 (4-15) at the third measurement (p trend = 0.002). In conclusion, the performance on the RFFT improved by repeating the test over an average follow-up period of three to six years. This practice effect was the largest in young adults and not dependent on educational level.