The SF-6D is a preference-based measure of health derived from the SF-36 that can be used for cos... more The SF-6D is a preference-based measure of health derived from the SF-36 that can be used for cost-effectiveness analysis using cost-per-quality adjusted life-year analysis. This study seeks to estimate a system weight for the SF-6D for Portugal and to compare the results with the UK system weights. Methods: A sample of 55 health states defined by the SF-6D has been valued by a representative random sample of the Portuguese population, stratified by sex and age (n = 140), using the Standard Gamble (SG). Several models are estimated at both the individual and aggregate levels for predicting health-state valuations. Models with main effects, with interaction effects and with the constant forced to unity are presented. Random effects (RE) models are estimated using generalized least squares (GLS) regressions. Generalized estimation equations (GEE) are used to estimate RE models with the constant forced to unity. Estimations at the individual level were performed using 630 health-state valuations. Alternative functional forms are considered to account for the skewed distribution of health-state valuations.
Nos últimos anos, têm sido desenvolvidos instrumentos de medição do estado de saúde e da qualidad... more Nos últimos anos, têm sido desenvolvidos instrumentos de medição do estado de saúde e da qualidade de vida obtida pela aplicação de programas de saúde, baseados na Teoria da Utilidade.
The use of preference-based generic instruments to measure the health-related quality of life of ... more The use of preference-based generic instruments to measure the health-related quality of life of a general population or of individuals suffering from a specific disease has been increasing. However, there are several discrepancies between instruments in terms of utility results. This study compares SF-6D and EQ-5D when administered to patients with cataracts and aims at explaining the differences. Agreement between EQ-5D and SF-6D health state classifications was assessed by correlation coefficients. Simple correspondence analysis was used to assess the agreement among the instrument’s descriptive systems and to investigate similarities between dimensions’ levels. Cluster analysis was used to classify SF-6D and EQ-5D levels into homogeneous groups. There was evidence of floor effects in SF-6D and ceiling effects in EQ-5D. Comparisons of means showed that SF-6D values exceeded EQ-5D values. Agreement between both instruments was high, especially between similar dimensions. However, different valuation methods and scoring algorithms contributed to the main differences found. We suggest that one or both instruments should be revised, in terms of their descriptive systems or their scoring algorithms, in order to overcome the weakness found.
Erratum to: Qual Life Res (2008) 17:1031–1042 DOI 10.1007/s11136-008-9368-8The last author’s affi... more Erratum to: Qual Life Res (2008) 17:1031–1042 DOI 10.1007/s11136-008-9368-8The last author’s affiliation was incorrectly specified in the original publication. The correct list of authors and their affiliations is shown below.
Purpose There has been an increasing interest in developing country-specific preference weights f... more Purpose There has been an increasing interest in developing country-specific preference weights for widely used measures of health-related quality of life. The valuation of health states has usually been done using cardinal preference elicitation techniques of standard gamble (SG) or time trade-off (TTO). Yet there is increasing interest in the use of ordinal methods to elicit health state utility values as an alternative to the more conventional cardinal techniques. This raises the issue of firstly whether ordinal and cardinal methods of preference elicitation provide similar results and secondly whether this relationship is robust across different valuation studies and different populations. Methods This study examines SG and rank preference weights for the SF-6D derived from samples of the UK and Portuguese general population. The preference weights for the Portuguese sample (n = 140) using rank data are estimated here with 810 health state valuations. The study further examines whether the use of these different preference weights has an impact when comparing the health of different age and severity groups in the Portuguese working population (n = 2,459). Results The rank model performed well across the majority of measures of goodness of fit used. The preference weights for the Portuguese sample using rank data are systematically lower than the UK weights for physical functioning and pain. Yet our results suggest higher similarity between preference weights derived using rank data than using standard gamble across the UK and Portuguese samples. Our results further suggest that the SF-6D values for a sample of the Portuguese working-age population and differences across groups are affected by the use of different preference weights. Conclusion We suggest that the use of a Portuguese SF-6D weighting system is preferred for studies aiming to reflect the health state preferences of the Portuguese population.
The SF-6D suffers from a floor effect where for patient groups in severe health a significant num... more The SF-6D suffers from a floor effect where for patient groups in severe health a significant number of patients report the lowest level of health possible for some dimensions, meaning the SF-6D cannot capture a deterioration in health for these patients. This paper presents a feasibility study aimed at reducing this floor effect. A modified SF-6D classification system was proposed that incorporated an additional level in each of the physical functioning and role limitations dimensions. The modified classification system was valued by a Portuguese general population sample (n = 140) using the Portuguese SF-6D protocol. A sample of 82 health states were valued and several regression models were estimated to produce preference weights to predict health state values for all states defined by the modified classification system. Estimations at the individual level were performed using 950 health state valuations. Models were analyzed in terms of logical consistency of coefficients, overall fit and predictive ability and were compared to Portuguese SF-6D models. The additional severity levels included in the modified classification system have significant decrements in health state values. These additional severity levels do not significantly impact on the modelled preference weights (the regression coefficients) of other levels across all dimensions. This feasibility study modified the SF-6D to reduce the floor effect. This study presents one option and further research in this area is encouraged.
The SF-6D is a preference-based measure of health derived from the SF-36 that can be used for cos... more The SF-6D is a preference-based measure of health derived from the SF-36 that can be used for cost-effectiveness analysis using cost-per-quality adjusted life-year analysis. This study seeks to estimate a system weight for the SF-6D for Portugal and to compare the results with the UK system weights. Methods: A sample of 55 health states defined by the SF-6D has been valued by a representative random sample of the Portuguese population, stratified by sex and age (n = 140), using the Standard Gamble (SG). Several models are estimated at both the individual and aggregate levels for predicting health-state valuations. Models with main effects, with interaction effects and with the constant forced to unity are presented. Random effects (RE) models are estimated using generalized least squares (GLS) regressions. Generalized estimation equations (GEE) are used to estimate RE models with the constant forced to unity. Estimations at the individual level were performed using 630 health-state valuations. Alternative functional forms are considered to account for the skewed distribution of health-state valuations.
Nos últimos anos, têm sido desenvolvidos instrumentos de medição do estado de saúde e da qualidad... more Nos últimos anos, têm sido desenvolvidos instrumentos de medição do estado de saúde e da qualidade de vida obtida pela aplicação de programas de saúde, baseados na Teoria da Utilidade.
The use of preference-based generic instruments to measure the health-related quality of life of ... more The use of preference-based generic instruments to measure the health-related quality of life of a general population or of individuals suffering from a specific disease has been increasing. However, there are several discrepancies between instruments in terms of utility results. This study compares SF-6D and EQ-5D when administered to patients with cataracts and aims at explaining the differences. Agreement between EQ-5D and SF-6D health state classifications was assessed by correlation coefficients. Simple correspondence analysis was used to assess the agreement among the instrument’s descriptive systems and to investigate similarities between dimensions’ levels. Cluster analysis was used to classify SF-6D and EQ-5D levels into homogeneous groups. There was evidence of floor effects in SF-6D and ceiling effects in EQ-5D. Comparisons of means showed that SF-6D values exceeded EQ-5D values. Agreement between both instruments was high, especially between similar dimensions. However, different valuation methods and scoring algorithms contributed to the main differences found. We suggest that one or both instruments should be revised, in terms of their descriptive systems or their scoring algorithms, in order to overcome the weakness found.
Erratum to: Qual Life Res (2008) 17:1031–1042 DOI 10.1007/s11136-008-9368-8The last author’s affi... more Erratum to: Qual Life Res (2008) 17:1031–1042 DOI 10.1007/s11136-008-9368-8The last author’s affiliation was incorrectly specified in the original publication. The correct list of authors and their affiliations is shown below.
Purpose There has been an increasing interest in developing country-specific preference weights f... more Purpose There has been an increasing interest in developing country-specific preference weights for widely used measures of health-related quality of life. The valuation of health states has usually been done using cardinal preference elicitation techniques of standard gamble (SG) or time trade-off (TTO). Yet there is increasing interest in the use of ordinal methods to elicit health state utility values as an alternative to the more conventional cardinal techniques. This raises the issue of firstly whether ordinal and cardinal methods of preference elicitation provide similar results and secondly whether this relationship is robust across different valuation studies and different populations. Methods This study examines SG and rank preference weights for the SF-6D derived from samples of the UK and Portuguese general population. The preference weights for the Portuguese sample (n = 140) using rank data are estimated here with 810 health state valuations. The study further examines whether the use of these different preference weights has an impact when comparing the health of different age and severity groups in the Portuguese working population (n = 2,459). Results The rank model performed well across the majority of measures of goodness of fit used. The preference weights for the Portuguese sample using rank data are systematically lower than the UK weights for physical functioning and pain. Yet our results suggest higher similarity between preference weights derived using rank data than using standard gamble across the UK and Portuguese samples. Our results further suggest that the SF-6D values for a sample of the Portuguese working-age population and differences across groups are affected by the use of different preference weights. Conclusion We suggest that the use of a Portuguese SF-6D weighting system is preferred for studies aiming to reflect the health state preferences of the Portuguese population.
The SF-6D suffers from a floor effect where for patient groups in severe health a significant num... more The SF-6D suffers from a floor effect where for patient groups in severe health a significant number of patients report the lowest level of health possible for some dimensions, meaning the SF-6D cannot capture a deterioration in health for these patients. This paper presents a feasibility study aimed at reducing this floor effect. A modified SF-6D classification system was proposed that incorporated an additional level in each of the physical functioning and role limitations dimensions. The modified classification system was valued by a Portuguese general population sample (n = 140) using the Portuguese SF-6D protocol. A sample of 82 health states were valued and several regression models were estimated to produce preference weights to predict health state values for all states defined by the modified classification system. Estimations at the individual level were performed using 950 health state valuations. Models were analyzed in terms of logical consistency of coefficients, overall fit and predictive ability and were compared to Portuguese SF-6D models. The additional severity levels included in the modified classification system have significant decrements in health state values. These additional severity levels do not significantly impact on the modelled preference weights (the regression coefficients) of other levels across all dimensions. This feasibility study modified the SF-6D to reduce the floor effect. This study presents one option and further research in this area is encouraged.
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Papers by Lara Ferreira