Page 75 - The value of total hip and knee arthroplasties for patients

Distinctiveness of Psychological Constructs
Introduction
Growing evidence supports the importance of psychological constructs in predicting outcomes of medical treatment including surgery.1;10;15;16;26;34;44 Usually epidemiological studies investigating the relationship between psychological factors and outcome of treatment restrict their assessment to one or two psychological questionnaires. However, in order to disentangle their unique contribution to outcome, the roles of separate constructs need to be explored simultaneously 37. It is therefore necessary that the instruments that aim to measure these constructs are able to discriminate between them.
Much attention has been given to the future oriented constructs ‘optimism’, 5 and ‘hope’.1;2 Both these constructs reflect expectancies about one’s future.
More specifically, optimism has been defined as “generalized positive outcome expectancies” 32 and hope as “a cognitive set that is based on a reciprocally derived
sense of successful agency (goal directed determination) and pathways (planning of ways to meet goals)”.40 Theory suggests that a hopeful person is more explicitly concerned with self-initiated actions that will enable him to achieve a favourable future while an optimistic person believes that somehow (through either internal or external factors) his future will be successful.25 Substantial empirical work investigating optimism and hope has been done within mental health settings. But evidence suggests these constructs may also be related to outcomes in medical treatments like surgery. For example: optimism explains close to 10% of the variance in post-surgical pain after total hip arthroplasty (THA) and total knee arthroplasty (TKA).30
Besides these general future oriented constructs interest in treatment specific psychological constructs like ‘treatment expectancy’ and ‘treatment credibility’ has also grown.36 Treatment expectancy is defined as “improvements that clients believe will be achieved” and treatment credibility as “how believable, convincing and logical the treatment is”.14 Conceptually, expectations for a given treatment may develop (at least partly) from how credible the treatment seems. Both these constructs may be related to treatment outcomes. For example it was found that expectancies about treatment outcome help predict return to work outcomes.22
While the abovementioned psychological constructs are grounded in different theoretical models, some studies have hypothesized that there is some conceptual
73