Confidence intervals for cost-effectiveness ratios: the use of 'bootstrapping'

Projected cost-effectiveness of ezetimibe/simvastatin compared with doubling the statin dose in the United Kingdom: findings from the INFORCE study

OBJECTIVE

To evaluate the incremental cost-effectiveness ratio (ICER) of switching to ezetimibe/simvastatin (Eze/Simva) compared with doubling the submaximal statin doses, in patients with acute coronary syndrome (ACS) events in the INFORCE study.

METHODS

Lifetime treatment costs and benefits were computed using a Markov model. Model inputs included each patient's cardiovascular risk factor profile and actual lipid values at baseline and 12 weeks (endpoint). Cardiovascular event and drug costs were discounted at 3.5%. Age-specific utilities were based on UK literature values and non-coronary heart disease mortality rates on the Office of National Statistics data. In the INFORCE study, 384 patients taking statins at stable doses for ≥6 weeks before hospital admission were stratified by statin dose/potency (low, medium, and high) and then randomized to doubling the statin dose or switching to Eze/Simva 10/40mg for 12 weeks.

RESULTS

The Eze/Simva group (n=195) had a higher mean baseline total cholesterol than the double-statin group (n=189). Analyses were adjusted for baseline characteristics. In the INFORCE study, Eze/Simva reduced low-density lipoprotein cholesterol (LDL-C) by ∼30% (vs. 4% with doubling statin doses) and significantly enhanced LDL-C goal attainment. In the cost-effectiveness analysis, Eze/Simva conferred 0.218 incremental discounted quality-adjusted life year (QALY) at a discounted incremental cost of £2524, for an ICER of £11,571/QALY (95% confidence interval=£8181-£18,600/QALY). The ICER was £13,552/QALY, £11,930/QALY, and £10,148/QALY in the low-, medium-, and high-potency strata, respectively.

CONCLUSIONS

Switching to Eze/Simva 10/40 mg is projected to be a cost-effective treatment (vs. double-statin) in UK patients with ACS.

Prospective randomized trial using cost–utility analysis of early versus delayed laparoscopic cholecystectomy for acute gallbladder disease

Background

This randomized controlled trial compared the cost–utility of early laparoscopic cholecystectomy with that for conventional management of newly diagnosed acute gallbladder disease.

Methods

Adults admitted to hospital with a first episode of biliary colic or acute cholecystitis were randomized to an early intervention group (36 patients, operation within 72 h of admission) or a conventional group (36, elective cholecystectomy 3 months later). Costs were measured from a National Health Service and societal perspective. Quality-adjusted life year (QALY) gains were calculated 1 month after surgery.

Results

The mean(s.d.) total costs of care were £5911(2445) for the early group and £6132(3244) for the conventional group (P = 0·928), Mean(s.d.) societal costs were £1322(1402) and £1461(1532) for the early and conventional groups respectively (P = 0·732). Visual analogue scale scores of health were 72·94 versus 84·63 (P = 0·012) and the mean(s.d.) QALY gain was 0·85(0·26) versus 0·93(0·13) respectively (P = 0·262). The incremental cost per additional QALY gained favoured conventional management at a cost of £3810 per QALY gained.

Conclusion

In this pragmatic trial, the cost–utilities of both the early and conventional approaches were similar, but the incremental cost per additional QALY gained favoured conventional management. Registration number: ISRCTN81663421 (http://www.controlled-trials.com).

Development of a decision support tool to facilitate primary care management of patients with abnormal liver function tests without clinically apparent liver disease [HTA03/38/02]. Abnormal Liver Function Investigations Evaluation (ALFIE)

BACKGROUND

Liver function tests (LFTs) are routinely performed in primary care, and are often the gateway to further invasive and/or expensive investigations. Little is known of the consequences in people with an initial abnormal liver function (ALF) test in primary care and with no obvious liver disease. Further investigations may be dangerous for the patient and expensive for Health Services. The aims of this study are to determine the natural history of abnormalities in LFTs before overt liver disease presents in the population and identify those who require minimal further investigations with the potential for reduction in NHS costs.

METHODS/DESIGN

A population-based retrospective cohort study will follow up all those who have had an incident liver function test (LFT) in primary care to subsequent liver disease or mortality over a period of 15 years (approx. 2.3 million tests in 99,000 people). The study is set in Primary Care in the region of Tayside, Scotland (pop approx. 429,000) between 1989 and 2003. The target population consists of patients with no recorded clinical signs or symptoms of liver disease and registered with a GP. The health technologies being assessed are LFTs, viral and auto-antibody tests, ultrasound, CT, MRI and liver biopsy. The study will utilise the Epidemiology of Liver Disease In Tayside (ELDIT) database to determine the outcomes of liver disease. These are based on hospital admission data (Scottish Morbidity Record 1), dispensed medication records, death certificates, and examination of medical records from Tayside hospitals. A sample of patients (n = 150) with recent initial ALF tests or invitation to biopsy will complete questionnaires to obtain quality of life data and anxiety measures. Cost-effectiveness and cost utility Markov model analyses will be performed from health service and patient perspectives using standard NHS costs. The findings will also be used to develop a computerised clinical decision support tool.

DISCUSSION

The results of this study will be widely disseminated to primary care, as well as G.I. hospital specialists through publications and presentations at local and national meetings and the project website. This will facilitate optimal decision-making both for the benefit of the patient and the National Health Service.

Cluster randomized trials: another problem for cost-effectiveness ratios

OBJECTIVES

This work has investigated under what conditions cost-effectiveness data from a cluster randomized trial (CRT) are suitable for analysis using a cluster-adjusted nonparametric bootstrap. The bootstrap's main advantages are in dealing with skewed data and its ability to take correlations between costs and effects into account. However, there are known theoretical problems with a commonly used cluster bootstrap procedure, and the practical implications of these require investigation.

METHODS

Simulations were used to estimate the coverage of confidence intervals around incremental cost-effectiveness ratios from CRTs using two bootstrap methods.

RESULTS

The bootstrap gave excessively narrow confidence intervals, but there was evidence to suggest that, when the number of clusters per treatment arm exceeded 24, it might give acceptable results. The method that resampled individuals as well as clusters did not perform well when cost and effectiveness data were correlated.

CONCLUSIONS

If economic data from such trials are to be analyzed adequately, then there is a need for further investigations of more complex bootstrap procedures. Similarly, further research is required on methods such as the net benefit approach.

Use of the bootstrap in analysing cost data from cluster randomised trials: some simulation results

Background

This work has investigated under what conditions confidence intervals around the differences in mean costs from a cluster RCT are suitable for estimation using a commonly used cluster-adjusted bootstrap in preference to methods that utilise the Huber-White robust estimator of variance. The bootstrap's main advantage is in dealing with skewed data, which often characterise patient costs. However, it is insufficiently well recognised that one method of adjusting the bootstrap to deal with clustered data is only valid in large samples. In particular, the requirement that the number of clusters randomised should be large would not be satisfied in many cluster RCTs performed to date.

Methods

The performances of confidence intervals for simple differences in mean costs utilising a robust (cluster-adjusted) standard error and from two cluster-adjusted bootstrap procedures were compared in terms of confidence interval coverage in a large number of simulations. Parameters varied included the intracluster correlation coefficient, the sample size and the distributions used to generate the data.

Results

The bootstrap's advantage in dealing with skewed data was found to be outweighed by its poor confidence interval coverage when the number of clusters was at the level frequently found in cluster RCTs in practice. Simulations showed that confidence intervals based on robust methods of standard error estimation achieved coverage rates between 93.5% and 94.8% for a 95% nominal level whereas those for the bootstrap ranged between 86.4% and 93.8%.

Conclusion

In general, 24 clusters per treatment arm is probably the minimum number for which one would even begin to consider the bootstrap in preference to traditional robust methods, for the parameter combinations investigated here. At least this number of clusters and extremely skewed data would be necessary for the bootstrap to be considered in favour of the robust method. There is a need for further investigation of more complex bootstrap procedures if economic data from cluster RCTs are to be analysed appropriately.

Strengthening health services to control epidemics: empirical evidence from Guinea on its cost-effectiveness

OBJECTIVE

To assess the cost-effectiveness of control measures implemented against epidemics in Guinea, West Africa.

METHODS

We collected all routine data available on incidence, mortality, control measures implemented and their cost during epidemics of cholera, measles and meningococcal meningitis in 1993-95. Then we estimated for one prefecture the effectiveness and cost-effectiveness of epidemic control measures for three scenarios: (i) 'natural' situation, (ii) 'routine' health services and (iii) 'intervention'. Where uncertainty was considerable, we used sensitivity analysis and estimated ranges.

FINDINGS

Routine health services reduced potential deaths by 51% (67%, 37% and 60% for cholera, measles and meningitis, respectively), and additional interventions further decreased potential deaths by 28% (28%, 27% and 30% for cholera, measles and meningitis, respectively). The marginal cost-effectiveness of epidemic control measures in routine health services was US dollars 29 per death averted. The marginal cost-effectiveness of additional interventions was US dollars 93 per death averted.

CONCLUSION

Even with the data weaknesses that characterize situations of epidemics it is possible to show that strengthening health services to control epidemics as was performed in Guinea was highly cost-effective. Moreover, sensitivity analysis over a range of assumptions confirms that (i) well-functioning health services averted the major part of avoidable deaths, (ii) combining existing health services with additional interventions minimizes the health impact of epidemics and (iii) case management should be a cornerstone of control of epidemics of cholera, measles and meningococcal meningitis.