Rater bias and the measurement of support needs.

Background: The development and use of support need instruments for funding disability services is a relatively recent initiative. Although the use of these measures appears at face value to provide an objective measure of support needs, little is known about their psychometric properties, particularly with respect to rater bias and purpose of assessment. A measure of support that has been developed in Australia to provide estimates of service needs and associated funding is the Service Need Assessment Profile (SNAP).

Method: This study investigated whether SNAP scores obtained for different assessment purposes - research and funding - are affected by rater bias, by comparing SNAP to 3 other measures of support from 29 people with intellectual disabilities.

Results: We found that SNAP scores completed for funding purposes showed an individual's support needs to be much greater than comparison scores on both SNAP and the 3 other measures obtained for research purposes.

Conclusions: Our results suggest that support measures such as SNAP may significantly overestimate support needs when raters know the assessment is being used for funding purposes.