Sophie A Derksen, Xenia Brancart, Gina Rossi Department of Psychology, Personality and Psychopathology Research Group (PEPS), Vrije Universiteit Brussel (VUB), Brussels, BelgiumCorrespondence: Sophie A Derksen, PE-PEPS, Vrije Universiteit Brussel (VUB), Pleinlaan 2, Brussels, 1050, Belgium, Email sophiederksen@outlook.comIntroduction: With a rapidly aging population, age-neutrality of psychological instruments is becoming ever more important for accurate assessment of older adults. This study aims to test the age-neutrality of the Dutch Behavioral Inhibition System/Behavioral Approach System (BIS/BAS) scales by means of Differential Item Functioning (DIF) and Differential Test Functioning (DTF) analyses.Methods: DIF and DTF analyses were conducted using an odds ratio approach. Potential DIF was examined for the two primary scales and three BAS subscales in 390 Dutch-speaking participants divided over three age groups.Results: Overall, the BIS-BAS scales lacked age-neutrality when comparing older adults to young adults: eight out of 20 items (ie, 40%) displayed DIF according to the adjusted Bonferroni corrected cut-offs, which exceeds the threshold of 25% for large DIF. Thus, for 40% of the test items, items were differently endorsed by young and older adults with the same position on the construct measured by the item. Therefore, the implications of the item-level DIF on the scale level were investigated across age groups. DTF analyses revealed large DTF for all BIS and BAS scales according to the adjusted Bonferroni corrected cut-offs.Discussion: DIF found in items on the BIS scale and BAS-Drive and BAS-Fun Seeking scale can probably be explained by a difference in degree of expression across age groups. A solution could be the development of age-specific norms. DIF on BAS-Reward Responsiveness subscale could be partly due to measuring a different construct across age groups. Rephrasing or replacing such items with DIF may increase age-neutrality of the BIS/BAS Scales.Keywords: older adults, BIS/BAS ...