SCREENING FOR STEREOPSIS WITHOUT THE USE OF TECHNICAL EQUIPMENT - SCALE DEVELOPMENT AND CROSS-VALIDATION

Background. Although adequate stereopsis is important for many common sensory-motor activities, large-scale normative samples of the relatio nship between stereopsis and other individual difference variables are relatively scarce, and stereopsis is often not routinely tested even in settings where it might play an important role, This is, in part, d ue to the fact that data collection requires individual testing, the u se of costly technical equipment and trained personnel. Method Beginni ng with a pool of 161 items and an initial sample of 542 individuals, we developed a self-report inventory-suitable for group testing, surve y administration or rapid individual screening-possessing a high corre lation with laboratory measures of stereopsis. The inventory was then cross-validated against laboratory measures of stereo-acuity in a sepa rate sample of 573 subjects. Results. For the combined samples, the re sulting 10-item Stereopsis Screening Inventory (SSI) correlated with l aboratory measures of per cent stereopsis (r = 0.80). The inventory's reliability was assessed with a resulting internal consistency coeffic ient (alpha) of 0.88. Conclusions. The SSI provides a fast, valid and inexpensive measure of uncorrected stereopsis which can be used for ra pid screening or epidemiological surveys. The correct classification r ate for the SSI was 84% for a low fence requiring 65% stereopsis or be tter, and 81% for a high fence of residual stereopsis of 25% or less. A conversion equation, with estimated variability is also provided for point estimates of per cent stereopsis from the SSI scores. A copy of the inventory and scoring procedure is given in the Appendix.