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- Modelling health state preference data using fixed and random effects modelsPublication . Ferreira, Lara Noronha; Ferreira, Pedro L.; Pereira, Luis NobreThe use of preference-based measures of health in the measurement of Health Related Quality of Life has become widely used in health economics. Hence, the development of preference-based measures of health has been a major concern for researchers throughout the world. This study aims to model health state preference data using a new preference-based measure of health (the SF- 6D) and to suggest alternative models for predicting health state utilities using fixed and random effects models. It also seeks to investigate the problems found in the SF-6D and to suggest eventual changes to it.
- O sistema português de valores do SF-6DPublication . Ferreira, Pedro L.; Ferreira, Lara Noronha; Pereira, Luis NobreIntrodução: Nos últimos tempos tem-se assistido ao desenvolvimento de estudos em alguns países, de forma a obter funções de valoração relativas aos instrumentos de medição de preferências mais utilizados. Na verdade, a evidência sugere que as valorações dos estados de saúde podem diferir de país para país. O objectivo deste estudo foi a determinação de um sistema de valores subjacente ao SF-6D para Portugal. Metodologia: Uma amostra de 55 estados de saúde definidos pelo SF-6D foi valorizada por uma amostra aleatória estratificada da população em geral, utilizando o standard gamble (SG). A pesquisa foi conduzida por entrevistas pessoais, tendo os respondentes valorizado seis estados de saúde, acrescidos do pior estado de saúde definido pelo SF-6D ou da morte imediata. Estimaram-se vários modelos com o objectivo de prever as valorações dos estados de saúde. Numa primeira fase, foram estimados modelos lineares, tanto ao nível individual, como agregado, assim como modelos com efeitos fixos, com efeitos principais e de interacção e com a constante forçada à unidade. Numa segunda fase, foram ainda testados, pelo método dos mínimos quadrados generalizados, modelos com efeitos aleatórios (MEA). Foram também estimados MEA com a constante forçada à unidade pelas equações de estimação generalizadas (EEG). Consideraram-se especificações alternativas, como forma de tomar em consideração o enviesamento das valorações dos estados de saúde. Os modelos foram analisados em termos dos seus coeficientes, ajustamento e capacidade para prever os valores dos estados de saúde captados pelo SG. Resultados: Os MEA e os modelos EEG produziram coeficientes significativos, que se verificou serem robustos nas especificações dos modelos. A utilização de uma bateria de medidas de bondade do ajustamento levou à conclusão que o modelo EEG com efeitos principais era o melhor modelo estimado. Conclusão: Esta investigação demonstra que é possível obter sistemas de pesos para a medição da qualidade de vida relacionada com a saúde. O melhor modelo obtido parece prever adequadamente os valores dos estados de saúde da população portuguesa. No entanto, existem algumas incoerências que devem ser investigadas.
- How consistent are health utility values?Publication . Ferreira, Pedro L.; Ferreira, Lara Noronha; Pereira, Luis NobreThe 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.
- An application of the SF-6D to create health values in Portuguese working age adultsPublication . Ferreira, Lara Noronha; Ferreira, Pedro L.; Pereira, Luis Nobre; Brazier, JohnObjectives : This study describes the health-related quality of life(HRQOL) of the Portuguese working age population and investigates sociodemographic differences. Methods : Subjects randomly selected from the working age population ( n =2,459) were assessed using the SF-36v2 and converted into the preference-based SF-6D. Results : The mean SF-6D utility value was 0.70 (range 0.63–0.73). The mean utility value was lower for the lower educational level than for the highest. Women, people living in rural areas and older adults reported lower levels of utility values. Non-parametric tests showed that health utility values were signifi cantly related to employment; unskilled manual workers reported utility values lower than non-manual workers. For different diseases, mean utility values ranged from 0.58 (sexual diseases) to 0.66 (hepatic conditions). Cluster analysis was adopted to classify individuals into three groups according to their answers to the SF-6D dimensions. Multinomial logit regression was used to detect sociodemographic characteristics affecting the probability of following each cluster pattern. This study yielded normative data by age and gender for the SF-6D. Conclusions: The authors conclude that SF-6D is an effective tool for measuring HRQOL in the community so that different population groups can be compared. The preference-based measure used seems to discriminate adequately across sociodemographic differences. These results allow a better understanding of the impact of sociodemographic variables on the burden of illness perception.
- A portuguese value set for the SF-6DPublication . Ferreira, Lara Noronha; Ferreira, Pedro L.; Pereira, Luis Nobre; Brazier, John; Rowen, DonnaObjectives: 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.Results: The models are analyzed in terms of their coefficients, overall fit, and the ability for predicting the SG-values. The RE models estimated using GLS and through GEE produce significant coefficients, which are robust across model specification. However, there are concerns regarding some inconsistent estimates, and so parsimonious consistent models were estimated. There is evidence of under prediction in some states assigned to poor health. The results are consistent with the UK results. Conclusion: The models estimated provide preference-based quality of life weights for the Portuguese population when health status data have been collected using the SF-36. Although the sample was randomly drowned findings should be treated with caution, given the small sample size, even knowing that they have been estimated at the individual level.