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Summary statistics for Patient-reported Outcome Measures: the improvement ratio

Szilard Nemes, Meridith E Greene, Erik Bulow, Ola Rolfson


Rationale, aims and objective: Patient-reported outcomes measures (PROMs) can facilitate objective comparisons of alternative treatments and can aid clinicians, researchers, decision-makers and members of the general public in gauging different healthcare providers’ performance. However, this assumes an easy to use and understand summary measure.

Methods: Using PROMs (EQ-5D index, EQ VAS and VAS Pain) from 1799 patients in 7 Swedish hospitals with at least 200 hip arthroplasty surgeries in 2009, we illustrated the possibility of summarizing pre- and post-treatment PROM values with the help of a simple index. This index expressed the attained improvement as a percentage of the total possible improvement. Change score, Cohen’s effect size and Standardized Response Means served as alternative measures.

Results: The Improvement Ratio index proved capable of offering a vivid and easy to understand summary of healthcare providers’ performance. The alternative measures indicated similar patterns as the Improvement Index. The routines of statistical inference made possible null-hypothesis testing of the improvement in different groups or testing for trends.

Conclusions: This simple improvement index gives an easy to understand summary measure that appeals not only to researchers, but also to laymen for consulting healthcare provider comparisons or countrywide white papers. We recommend using the Improvement Ratio index to summarize the PROMs outcome of elective surgeries.


Arthoplasty, measurement precision, outcome interpretation, Patient-reported Outcome Measures, person-centered healthcare, quality improvement, socioeconomic factors

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Rolfson, O., Karrholm, J., Dahlberg, L.E. & Garellick, G. (2011). Patient-reported outcomes in the Swedish Hip Arthroplasty Register. Results of a nationwide prospective observational study. Journal of Bone Joint Surgery British Volume 93B (7) 867-875.

Rolfson, O., Rothwell, A., Sedrakyan, A., Chenok, K.E., Bohm, E., Bozic, K.J. & Garellick, G. (2011) Use of Patient-Reported Outcomes in the Context of Different Levels of Data. Journal of Bone & Joint Surgery American Volume 93 (Supplement 3) 66-71.

Black, N. (2013). Patient reported outcome measures could help transform healthcare. British Medical Journal 346, f167.

Davidson, M. & Keating, J. (2014). Patient-reported outcome measures (PROMs): how should I interpret reports of measurement properties? A practical guide for clinicians and researchers who are not biostatisticians. British Journal of Sports Medicine 48 (9) 792-796.

Sapyta, J., Riemer, M. & Bickman, L. (2005). Feedback to clinicians: Theory, research, and practice. Journal of Clinical Psychology 61 (2) 145-153.

Smith, P.C. & Street, A.D. (2013). On the uses of routine patient-reported health outcome data. Health Economics 22 (2) 119-131.

Mokkink, L.B., Terwee, C.B., Knol, D.L., Stratford, P.W., Alonso, J., Patrick, D.L., Bouter, L.M. & de Vet, H.C. (2006). Protocol of the COSMIN study: COnsensus-based Standards for the selection of health Measurement INstruments. BMC Medical Research Methodology 6:2.

Mokkink,. L.B., Terwee, C.B., Knol, D.L., Stratford, P.W., Alonso, J., Patrick, D.L., Bouter, L.M. & de Vet, H.C. (2010). The COSMIN checklist for evaluating the methodological quality of studies on measurement properties: A clarification of its content. BMC Medical Research Methodology 10, 22.

Mokkink, L.B., Terwee, C.B., Patrick, D.L., Alonso, J., Stratford, P.W., Knol, D.L., Bouter, L.M. & de Vet, H.C. (2010). The COSMIN study reached international consensus on taxonomy, terminology, and definitions of measurement properties for health-related patient-reported outcomes. Journal of Clinical Epidemiology 63 (7) 737-745.

Mokkink, L.B., Terwee, C.B., Patrick, D.L., Alonso, J., Stratford, P.W., Knol, D.L., Bouter, L.M. & de Vet, H.C.W. (2010). The COSMIN checklist for assessing the methodological quality of studies on measurement properties of health status measurement instruments: an international Delphi study. Quality of Life Research 19 (4) 539-549.

Terwee, C.B., Mokkink, L.B., Knol, D.L., Ostelo, R.W.J.G., Bouter, L.M. & de Vet, H.C.W. (2012). Rating the methodological quality in systematic reviews of studies on measurement properties: a scoring system for the COSMIN checklist. Quality of Life Research 21 (4) 651-657.

Lund, E. & Gram, I.T. (1998). Response rate according to title and length of questionnaire. Scandinavian Journal of Public Health 26 (2) 154-160.

Hildon, Z., Allwood, D. & Black, N. (2015). Patients' and clinicians' views of comparing the performance of providers of surgery: a qualitative study. Health Expectations 18 (3) 366-378.

Hildon, Z., Neuburger, J., Allwood, D., van der Meulen, J. & Black, N. (2012). Clinicians' and patients' views of metrics of change derived from patient reported outcome measures (PROMs) for comparing providers' performance of surgery. BMC Health Services Research 12 (1) 171.

Hildon, Z., Allwood, D. & Black, N. (2012). Making data more meaningful: Patients' views of the format and content of quality indicators comparing health care providers. Patient Education and Counseling 88 (2) 298-304.

Terwee, C.B., Dekker, F.W., Wiersinga, W.M., Prummel, M.F. & Bossuyt, P.M.M. (2003). On assessing responsiveness of health-related quality of life instruments: Guidelines for instrument evaluation. Quality of Life Research 12 (4) 349-362.

Norman, G.R., Wyrwich, K. & Patrick, D. (2007). The mathematical relationship among different forms of responsiveness coefficients. Quality of Life Research 16 (5) 815-822.

Shah, S., Vanclay, F. & Cooper, B. (1990). Efficiency, effectiveness, and duration of stroke rehabilitation. Stroke 21 (2) 241-246.

Chang, V.T., Sorger, B., Rosenfeld, K.E., Lorenz, K.A., Bailey, A.F., Bui, T., Weinberger, L. & Montagnini, M. (2007). Pain and palliative medicine. Journal of Rehabilitation Research & Development 44 (2) 279-294.

Arden, N.K., Kiran, A., Judge, A., Biant, L.C., Javaid, M.K., Murray, D.W., Carr, A.J., Cooper, C. & Field, R.E. (2011). What is a good patient reported outcome after total hip replacement? Osteoarthritis and Cartilage 19 (2) 155-162.

Grasso, M.G., Troisi, E., Rizzi, F., Morelli, D. & Paolucci, S. (2005). Prognostic factors in multidisciplinary rehabilitation treatment in multiple sclerosis: an outcome study. Multiple Sclerosis 11 (6) 719-724.

Ver Hoef, J.M. (2012). Who Invented the Delta Method? The American Statistician 66 (2) 124-127.

Nemes, S., Parris, T.Z., Danielsson, A., Einbeigi, Z., Steineck, G., Jonasson, J.M. & Helou, K. (2013). Integrative Genomics with Mediation Analysis in a Survival Context. Computational and Mathematical Methods in Medicine 2013, 8.

Carpenter, J. & Bithell, J. (2000). Bootstrap confidence intervals: when, which, what? A practical guide for medical statisticians. Statistics in Medicine 19 (9) 1141-1164.

Bickel, P.J. & Freedman, D.A. (1984). Asymptotic Normality and the Bootstrap in Stratified Sampling. Annals of Statistics 12 (2) 470-482.

Rao, J.N.K. & Wu, C.F.J. (1988). Resampling Inference With Complex Survey Data. Journal of the American Statistical Association 83 (401) 231-241.

Kiran, A., Hunter, D.J., Judge, A., Field, R.E., Javaid, M.K., Cooper, C., Arden, N.K. & Oxford NDORMS Musculoskeletal Epidemiology Unit Writing Committee. (2014). A Novel Methodological Approach for Measuring Symptomatic Change Following Total Joint Arthroplasty. Journal of Arthroplasty 29 (11) 2140-2145.

Rao, T.J. (2002). Mean of ratios or ratio of means or both? Journal of Statistical Planning and Inference 102 (1) 129-138.

EuroQolGroup. (1990). EuroQol - a new facility for the measurement of health-related quality of life. Health Policy 16 (3) 199-208.

Wittrup-Jensen, K.U., Lauridsen, J., Gudex, C. & Pedersen, K.M. (2009). Generation of a Danish TTO value set for EQ-5D health states. Scandinavian Journal of Public Health 37 (5) 459-466.

Paulsen, A., Roos, E.M., Pedersen, A.B. & Overgaard, S. (2014). Minimal clinically important improvement (MCII) and patient-acceptable symptom state (PASS) in total hip arthroplasty (THA) patients 1 year postoperatively. Acta Orthopaedica 85 (1) 39-48.

Grandy, S., Fox, K. & Group tSS. (2012). Change in health status (EQ-5D) over 5 years among individuals with and without type 2 diabetes mellitus in the SHIELD longitudinal study. Health and Quality of Life Outcomes 10 (1) 99.

Swartz, R., Schwartz, C., Basch, E., Cai, L., Fairclough, D., McLeod, L., Mendoza, T. & Rapkin, B. (2011). The king’s foot of patient-reported outcomes: current practices and new developments for the measurement of change. Quality of Life Research 20 (8) 1159-1167.

Norman, G.R., Sloan, J.A. & Wyrwich, K.W. (2003). Interpretation of Changes in Health-related Quality of Life: The Remarkable Universality of Half a Standard Deviation. Medical Care 41 (5) 582-592.

Whynes, D. (2013). Does the correspondence between EQ-5D health state description and VAS score vary by medical condition? Health and Quality of Life Outcomes 11 (1) 155.

Wilke, S., Janssen, D., Wouters, E., Schols, J., Franssen, F. & Spruit, M. (2012). Correlations between disease-specific and generic health status questionnaires in patients with advanced COPD: a one-year observational study. Health and Quality of Life Outcomes 10 (1) 98.

Allwood, D., Hildon, Z. & Black, N. (2013). Clinicians' views of formats of performance comparisons. Journal of Evaluation in Clinical Practice 19 (1) 86-93.



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