Early pilot stress report systems were adapted and modified from existing psychological questionnaires and surveys. The data from these pilot-specific surveys is then processed and analyzed through an aviation-focused system or scale. Pilot-oriented questionnaires are generally designed to study work stress or home stress. Self-report can also be used to measure a combination of home stress, work stress, and perceived performance. A study conducted by Fiedler, Della Rocco, Schroeder and Nguyen (2000) used Sloan and Cooper's modification of the Alkov questionnaire to explore aviators' perceptions of the relationship between different types of stress. The results indicated that pilots believed performance was impaired when home stress carried over to the work environment. The degree of home stress that carried over to work environment was significantly and negatively related to flying performance items, such as planning, control, and accuracy of landings. The questionnaire was able to reflect pilots' retroactive perceptions and the accuracy of these perceptions.