Generic PROMs aim to assess all dimensions of health-related quality of life. The World Health Organization Quality of Life Group has recommended that
39 5 dimensions are assessed in any generic quality of life survey: physical health, psychological health, social relationship perceptions, function and well-being. Commonly used generic PROMs in orthopaedic literature include the Medical Outcomes Study 36-Item Short Form Health Survey (SF-36), the Medical Outcomes Study 12-Item Short Form Health Survey (SF-12), the Nottingham Health Profile (NHP) and the European Quality of Life 5-Dimension (Euroqol) questionnaire.
1.6.6.1.1 The Medical Outcomes Study 36-Item Short Form Health Survey (SF-36)
SF-36 is a multi-purpose questionnaire used to measure general health status40. It was originally developed in American English. A United Kingdom English version is now available. The questionnaire refers to health over the previous 4 weeks but a more acute version that refers to health over the previous week is available. The questionnaire contains 36 questions each of which has between 2 and 6 answers. Each answer is awarded a score of between 0 (indicating poor health) and 100 (indicating good health). The questions are grouped into one of eight health concepts: bodily pain (BP), physical functioning (PF), role limitations due to physical health (RP), general health (GH), mental health (MH), vitality (VT), social functioning (SF) and role limitations due to emotional health (RE). There is also a health transition question that does not contribute to any of the 8 domains.
40 The 8 health concepts can be further amalgamated into 2 higher order groups. These are known as the Physical Component Summary (PCS) and the Mental Component Summary (MCS). The PCS is calculated from the BP, PF, RP and GH scores. It is most responsive to treatments that alter physical symptoms such as hip arthroplasty. The MCS is calculated from the MH, VT, SF and RE scores and is most responsive to drugs and therapies that target psychiatric disorders. Three of the scales (VT, GH and SF) have significant correlation with both the physical and mental summary measures.
SF-36 takes approximately 10 minutes to complete. It is proven to be suitable for self-administration, computerized administration or administration by an interviewer either in person or by telephone. Scores are calculated by summated ratings and standardised SF-36 algorithms. Individual question scores are summated without standardisation or weighting. Standardisation is avoided by using questions with roughly similar means and standard deviations, and weighting is avoided by selecting equally representative questions.
SF-36 has been evaluated in several studies. It is proven to be valid and reliable41,42, sensitive and reproducible40. It has been used in over 4,000
publications assessing over 200 different diseases. SF-36 has been specifically investigated in patients undergoing hip arthroplasty where it was shown to be both valid43 and reliable44. However, these studies also showed that SF-36 has minor ‘floor’ and ‘ceiling’ effects45,46. ‘Floor’ effect refers to the situation where a questionnaire is unable to measure a negative value that is lower than the
41 range provided in the choice of answers. In this situation, if a patient reports the lowest value for a question and then deteriorates further, the deterioration will not be detected by the questionnaire. ‘Ceiling’ effect refers to the opposite situation, where a questionnaire is unable to measure a positive value that is higher than the range provided in the choice of answers. In this situation, if a patient reports the highest value for a question and then improves, the
improvement will not be detected by the questionnaire.
1.6.6.1.2 The Medical Outcomes Study 12-Item Short Form Health Survey (SF-12)
SF-1247 is an abridged version of SF-36 containing 12 out of the 36 questions. SF-12 questions can be amalgamated to produce profiles of the eight SF-36 health concepts but only if the sample size is sufficiently large. SF-12 scores are calculated using weighted algorithms (i.e. the questions in SF-12 contribute different values to the overall score, unlike SF-36) and a computer program is available for this calculation.
The main advantage of SF-12 over SF-36 is that it is shorter. It is therefore quicker for patients to complete and quicker for research personnel to record and analyse data. A disadvantage is that a computer program is necessary for scoring each survey. A further disadvantage of SF-12 is that it has less
construct validity and sensitivity than SF-36, producing less precise scores for the 8-scale health profile47. This is less important in large group studies since
42 the confidence intervals are largely determined by sample size but could result in insignificant findings in smaller studies.
1.6.6.1.3 Nottingham Health Profile (NHP)
The Nottingham Health Profile (NHP) is a self-administered questionnaire that takes 5 to 10 minutes to complete. It was developed in United Kingdom English and consists of 2 parts. Part I contains 38 'yes/no' items covering 6 dimensions: pain, physical mobility, emotional reactions, energy, social isolation and sleep. Part II contains 7 'yes/no' questions concerning activities of daily living. Each part is scored using weighted values giving a score of 0 (no problems at all) to 100 (presence of maximal problems). The two parts can be used
independently. The NHP is proven to be internally consistent, valid,
reproducible and sensitive48. No psychometric analysis of the NHP has been performed on patients undergoing hip or knee arthroplasty.
Overall, the NHP has one major disadvantage when compared to SF-36 concerning the response format. The NHP uses dichotomous 'yes/no'
responses, where as SF-36 has several choices for each response. This allows the SF-36 to detect positive as well as negative states of health. The NHP often explores only ill health. A patient with an initial acceptable NHP score who makes an obvious clinical improvement may fail to show a change in the NHP score. Furthermore, a false negative response is more likely with the NHP when a patient with good function must respond on a scale that only assesses dysfunction. The dichotomous NHP response format produces higher 'ceiling'
43 effects in all dimensions when compared to SF-3649. They both have equal minor 'floor' effects.
1.6.6.1.4 EuroQol
The EuroQol (EQ-5D)50 questionnaire contains 2 pages. There are 15
questions on the first page regarding 5 aspects of general health: mobility, self- care, usual activities, pain and depression. Each question has 3 possible answers: ‘no problem’, ‘moderate problem’ or ‘extreme problem’. The second page of EuroQol aims to elucidate the overall health of the patient. It contains a visual analogue scale with 0 indicating the worst possible health and 100
indicating the best possible health.
EuroQol was designed to be self-administered and takes 5 minutes to complete. It has been shown in studies to be both valid51 and reliable52. However,
EuroQol suffers from ‘ceiling’ effects due to the restricted response format. This effect is partially overcome by the use of the visual analogue scale on the
second page. There is limited psychometric analysis of the questionnaire in patients undergoing hip and knee arthroplasty. Test-retest reliability has been shown53 and there is some evidence of construct validity and responsiveness54.