BACKGROUND:Decentralisation of social support and budget cuts spurred interest in outcome-oriented payment systems in the Netherlands. Hence, measurement of relevant outcomes, such as self-reliance and participation, is needed. The Impact on Participation and Autonomy (IPA) questionnaire for rehabilitation clients was adapted for social support, called IPA-MO, and its validity and reliability were tested among social support clients in eight municipalities in 2014 and 2016. METHODS:The total research sample comprised of 4120 persons. Homogeneous subgroups were distinguished based on 1) disability and 2) age. Exploratory factor analysis (PCF) was used to identify domains for IPA-MO. Model fit was assessed with Confirmatory Factor Analysis (CFA) using structural equation modelling. RESULTS:PCF revealed that the IPA-MO model consists of all five original IPA domains: Autonomy indoors, Family role, Autonomy outdoors, Social life and relations, and Work and education. As a result of new items added, a new, sixth domain was developed: Financial autonomy. Due to high non-response on Work & education, construct validity was first tested for a five-domain IPA-MO model. The composition of the IPA-MO domains showed slight differences: the item on 'mobility indoor' shifted from Autonomy indoors (IPA) to Family Role in IPA-MO. The item on reciprocity shifted from Social Life and relations (IPA) to Autonomy outdoors (IPA-MO). Internal reliability was confirmed for all domains (Cronbach's alpha >.80). CFA showed acceptable construct validity of the five-domain IPA-MO model for the social support population (CFI .936, TLI .925, SRMR .051), all age groups and most disability-based groups. Construct validity including Work & education was tested for 234 participants. Then, PCF revealed six domains and the model fit was acceptable (CFI .915, TLI .903, SRMR .067). CONCLUSIONS:IPA-MO is a valid and reliable instrument to assess outcomes of social support. Further research on the domain Financial autonomy is needed. Social-support clients are numerous and dispersed and, in spite of the best intentions, hard to involve widely in policy processes. A valid outcome measure offers municipalities possibilities to gain insight in social costs and benefits of new policies. Outcome measurement also allows to contract bundled-services of providers, thereby changing the incentives for providers from increasing production to much needed innovation. Taking the perceptions of autonomy and participation of social-support clients as the acid test for the effectiveness of social support policies, may prove a serious game-changer in politics.