Reliability of a Measure of Perceived Functional Ability

///Reliability of a Measure of Perceived Functional Ability
Reliability of a Measure of Perceived Functional Ability 2017-05-20T18:23:01+00:00

Matheson LN, Matheson ML, Grant J. Development of a measure of perceived functional ability. Journal of Occupational Rehabilitation, 1993;3(1), 15–30.


The impaired individual’s sense of competence appears to be an important determinant of his or her ability to benefit from rehabilitation. White (1959) defined competence in terms of the individual’s efficacy in meeting environmental demands. White posited that humans have an intrinsic drive to influence the environment. This “urge towards competence” provides motivation for exploring, manipulating, and acting on the environment. Functional competence is defined by the individual in terms of his or her ability to control the immediate social and physical environment. Functional self-efficacy is based on the individual’s perception of this competence. Bandura (1977 and 1982) postulated that self-referent thought affects psychosocial function. Individuals’ perception of their abilities affect how they behave, their level of motivation, thought processes, and emotional reactions to challenging circumstances. Bandura argues that the individual’s perception of functional self-efficacy is an important component of motivation in that it encourages the individual to attempt new activities and limits the individual from attempting tasks that may be dangerous or risky. The impaired individual’s perception of functional self-efficacy arises from experience. Christiansen (1991) reports that “the extent to which individuals are able to develop a positive sense of self and belief in their autonomy is largely based on their successes in dealing with environmental challenges….”

Several instruments have been developed to measure the disabled individual’s self-perception. However, none of these instruments focus on manual material handling tasks or on activities of daily living which place particular emphasis on the spine. In response, the Spinal Function Sort was developed. The purpose of the SFS is to quantify the disabled individual’s perception of his or her ability to perform work tasks that involve the use of the spine in various ways. This can be useful to provide a baseline measure of the individual’s perception of function prior to the onset of therapeutic intervention. This study investigated the reliability and validity of the SFS across a broad range of application sites.


Six occupational rehabilitation clinics agreed to participate. All were established clinics with ongoing functional capacity evaluation, work hardening, and work conditioning programs. A total of 180 subjects agreed to participate in the study: 126 males and 54 females. Most of the subjects (93% of those reporting) had a spinal soft tissue injury as the primary site/diagnosis. Subjects ranged in age from 20 years to 76 years with an average age of 37.0 years (SD = 9.9). Subjects ranged in chronicity in terms of number of days since injury from 8 days to 3422 days with an average of 379 days (SD = 564). Most subjects (94%) were able to be retested within one week of the initial test. Overall, the average test-retest delay was 3.2 days.


Gender and Perceived Capacity: A significant difference on each SFS test administration between males and females was found. A two-factor repeated measures analysis of variance (test administration x gender) on rating of perceived capacity revealed a statistically significant difference across gender (F1,177 = 8.05, p = .005). There was also a significant difference between the first and second administrations of the SFS tests, with the retest yielding consistently higher scores across gender (F1,177 = 28.61, p = .001). No interaction effects were observed (F1,177 = .07, p = .78).

Effect of Chronicity on Self Perception: In order to investigate the possibility of an effect on RPC due to degree of chronicity, a simple classification scheme was developed after review of a frequency distribution based on number of days since injury. A significant difference across four degrees of chronicity was found in terms of age in a one-factor analysis of variance (F3,169 = 6.58, p < .001). No difference was found based on number of days between test and retest (F3,169 = .42, p = .73). A subsequent two-factor repeated measures analysis of variance on RPC score reveals a statistically significant difference based on degree of chronicity (F3,168 = 2.67, p = .05). Of considerable interest is that the interaction between degree of chronicity and test administration is significant (F3,168 = 2.85, p = .04).


This research establishes the reliability across a variety of application sites of a new instrument that is intended to evaluate the functional self-efficacy of disabled individuals. While designed as a reliability study, the present study also found that chronicity is related to diminished functional self-efficacy. It may be a direct causal relationship in which greater chronicity leads to lower functional self-efficacy. Subjects who received intervention earlier have significantly higher initial ratings of perceived capacity than subjects who received intervention later. However, another interpretation of these data is that a low score on the SFS may be a characteristic of individuals who eventually become chronically disabled. That is, lower functional self-efficacy leads to greater chronicity. At a level below that which would be considered necessary for involvement in each individual’s usual and customary occupation, the rating of perceived capacity may be interpreted by the individual as an indicator of functional inefficacy, incompetence, or helplessness. If this is so, the SFS may be a useful tool to provide early identification of those who may need more intense treatment.

In addition to the unexpected finding that chronicity is related to functional self-efficacy, there were two other unexpected findings in the present study. The first was the degree to which functional self-efficacy is reactive to the functional capacity evaluation process. On average, each subject’s rating of perceived capacity improved by 9% with only the experience of the functional capacity evaluation separating the first test administration from the second. This may be a reaction to the initial administration of the SFS or it may be due to other factors commonly found in the functional capacity evaluation process. In any case, the change is in a “positive” direction and is consistent across sites, given allowances for chronicity. The second unexpected finding was the degree to which this reactivity in functional self-efficacy differs with chronicity. That is, significant improvement in functional self-efficacy was found among subjects who were within one year of the disabling injury. Beyond that point in time, functional self-efficacy is not only lower but is less likely to respond to these levels of intervention. If functional self-efficacy is to be improved, it will require more intense intervention.