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Cost-effectiveness analysis of colorectal cancer screening strategies in Singapore: a dynamic decision analytic approach |
Wong S S, Leong A P, Leong T Y |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology Five screening strategies for the detection of colorectal cancer (CRC) in the general population were examined. The strategies were guaiac faecal occult blood test (FOBT), immunochemical FOBT (FOBT-IMM), double contrast barium enema (DCBE), flexible sigmoidoscopy (FSIG), and colonoscopy (COL). FOBT and FOBT-IMM, if negative, were repeated yearly, FSIG every 3 years, DCBE every 5 years, and COL every 10 years. Individuals who tested positive with FOBT, FOBT-IMM, DCBE, and FSIG underwent COL for confirmation.
Economic study type Cost-effectiveness analysis.
Study population The study population comprised a hypothetical cohort of individuals aged 50 to 70 years in the general population.
Setting The setting was not explicitly reported, but it might have been primary care. The economic study was carried out in Singapore.
Dates to which data relate Some of the effectiveness evidence was derived from a study published in 1995. No explicit dates for resource use were reported. The price year was not reported.
Source of effectiveness data The effectiveness evidence was derived from a synthesis of published studies and experts' opinions.
Modelling A semi-Markov model was constructed to simulate the natural history of the disease, and to examine the impact of the five screening strategies on costs and survival in a hypothetical cohort of individuals from the general population. The time horizon of the model was 50 years. The starting age of the patients was 50 years. After a positive result in one of the screening strategies, patients underwent COL. If COL was negative, the patients re-entered screening in 10 years' time. If COL was positive to polyps, the patients entered a polyp follow-up protocol. If COL was positive for cancer, then patients underwent surgery depending on the cancer stage. Examples of possible health states were given in the article and the model was illustrated in detail.
Outcomes assessed in the review The outcomes estimated from the literature were:
the complication rates,
the incidence of cancer and 5-year survival,
sensitivity and specificity, and
age distribution.
Study designs and other criteria for inclusion in the review Sources searched to identify primary studies Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Number of primary studies included The authors explicitly reported the use of two primary studies, but other published sources also appear to have been used.
Methods of combining primary studies Investigation of differences between primary studies Results of the review Complications associated with FSIG and COL:
the rate of bleeding was 0.0001 with FSIG and 0.001 with COL;
the rate of perforation was 0 with FSIG and 0.0007 with COL; and
the rate of death was 0 with FSIG and 0.00005 with COL.
The incidence of polyps was 0.234.
The incidence of Dukes A and B was 0.0001385, the incidence of Dukes C and D was 0.0001835, and the incidence of total Dukes A to D was 0.0003220.
The 5-year survival rate was 0.99 with polyps, 0.8 with Dukes A and B, and 0.2 with Dukes C and D.
The sensitivity of FOBT was 0.1 for polyps and 0.6 for cancer, while the specificities were 0.9 for polyps and for cancer.
The sensitivity of FOBT-IMM was 0.4 for polyps and 0.9 for cancer, while the specificities were 0.95 for polyps and for cancer.
The sensitivity of DCBE was 0.3 for polyps and 0.7 for cancer, while the specificities were 0.9 for polyps and for cancer.
The sensitivity of FSIF for polyps or cancer was 0.6 and the specificity was 0.98.
The sensitivity of COL for polyps or cancer was 0.9 and the specificity was 1.
The age distribution of the participants was 39% in the 50- to 54-year age group, 22% in the 55- to 59-year age group, 22% in the 60- to 64-year age group, and 17% in the 65- to 69-year age group.
Methods used to derive estimates of effectiveness Some assumptions, based on the expert opinions of local surgeons, were made.
Estimates of effectiveness and key assumptions Experts' opinions were mixed with data derived from the literature (see Results of the Review). The compliance rate was assumed to be 100%.
Measure of benefits used in the economic analysis The summary benefit measure was life expectancy. This was obtained from the decision model. Discounting does not appear to have been applied. Life expectancy for 'no screening' was computed by setting the value for compliance to zero. The resultant value, 76.32 years, was the life-expectancy of the population without any screening programme.
Direct costs Discounting does not appear to have been carried out, although it would have been methodologically relevant due to the long timeframe of the model. The unit costs were presented separately from the quantities of resources used. The health services included in the economic evaluation were the screening procedures (including histology with FSIG and COL) and other procedures related to complications and treatment (i.e., COL with polypectomy, cancer resection, and the treatment of complications associated with COL). The cost/resource boundary of the study was not reported. Resource use was mainly estimated on the basis of assumptions. The costs were derived from the schedule of charges for a non-subsidised patient in Singapore restructured hospitals. The price year was not reported.
Statistical analysis of costs The costs were treated deterministically.
Indirect Costs The indirect costs were not considered in the economic evaluation.
Currency Singapore dollars (SGD$).
Sensitivity analysis Sensitivity analyses were not carried out.
Estimated benefits used in the economic analysis The life expectancy by age group and screening strategy was:
in the age group 50 - 54 years, 25.56 years for FOBT, 25.50 years for FOBT-IMM, 25.79 years for FSIG, 26.03 years for DCBE, and 25.71 years for COL;
in the age group 55 - 59 years, 21.44 years for FOBT, 21.42 years for FOBT-IMM, 21.74 years for FSIG, 21.95 years for DCBE, and 21.94 years for COL;
in the age group 60 - 64 years, 17.67 years for FOBT, 17.69 years for FOBT-IMM, 18.02 years for FSIG, 18.19 years for DCBE, and 17.92 years for COL;
in the age group 65 - 69 years, 14.27 years for FOBT, 14.31 years for FOBT-IMM, 14.56 years for FSIG, 14.73 years for DCBE, and 14.92 years for COL.
Cost results The estimated costs by age group and screening strategy were:
in the age group 50 - 54 years, SGD$501.82 with FOBT, SGD$1,050.08 with FOBT-IMM, SGD$1,139.31 with FSIG, SGD$786.34 with DCBE, and SGD$1,252.03 with COL;
in the age group 55 - 59 years, SGD$382.33 with FOBT, SGD$893.61 with FOBT-IMM, SGD$922.24 with FSIG, SGD$618.75 with DCBE, and SGD$1,218.09 with COL;
in the age group 60 - 64 years, SGD$252.31 with FOBT, SGD$688.82 with FOBT-IMM, SGD$675.83 with FSIG, SGD$442.56 with DCBE, and SGD$724.56 with COL;
in the age group 65 - 69 years, SGD$103.08 with FOBT, SGD$340.49 with FOBT-IMM, SGD$365.40 with FSIG, SGD$259.26 with DCBE, and SGD$718.17 with COL.
The cost of no screening was implicitly assumed to be SGD$0.
Synthesis of costs and benefits Incremental cost-effectiveness ratios were calculated to compare the costs and benefits of the screening strategies with the no screening option (based on a life expectancy of 76.32 years for patients who received no screening). The methods used to calculate these incremental ratios were described in the article.
The incremental cost per life-year saved by age group and screening strategy was:
in the age group 50 - 54 years, SGD$288.33 with FOBT, SGD$623.12 with FOBT-IMM, SGD$576.28 with FSIG, SGD$355.07 with DCBE, and SGD$660.35 with COL;
in the age group 55 - 59 years, SGD$145.70 with FOBT, SGD$342.75 with FOBT-IMM, SGD$315.53 with FSIG, SGD$197.19 with DCBE, and SGD$390.24 with COL;
in the age group 60 - 64 years, SGD$65.42 with FOBT, SGD$177.69 with FOBT-IMM, SGD$160.81 with FSIG, SGD$101.17 with DCBE, and SGD$176.51 with COL;
in the age group 65 - 69 years, SGD$18.89 with FOBT, SGD$62.03 with FOBT-IMM, SGD$63.60 with FSIG, SGD$43.86 with DCBE, and SGD$117.72 with COL.
The weighted incremental cost-effectiveness ratio (with respect to no screening) was SGD$162.11 with FOBT, SGD$368.06 with FOBT-IMM, SGD$340.36 with FSIG, SGD$211.57 with DCBE, and SGD$402.24 with COL. The weighted incremental ratios were obtained using the age distribution data for each age group.
Authors' conclusions All the screening strategies improved patient survival, but the faecal occult blood test (FOBT) offered the most acceptable cost-effectiveness ratio.
CRD COMMENTARY - Selection of comparators The rationale for the choice of the comparators was clear. All interventions represented possible screening options in the authors' setting. The no screening strategy was also considered to be a better representation of the additional costs and life expectancy of the screening interventions. You should decide whether they are valid comparators in your own setting.
Validity of estimate of measure of effectiveness The effectiveness evidence came from experts' opinions and data derived from the literature. However, it was not possible to distinguish which data were derived from the literature and which from experts' assumptions. In addition, it was not stated whether a systematic review of the literature had been undertaken and the primary studies appear to have been identified selectively. The uncertainty around these data was not investigated in a sensitivity analysis. The authors also acknowledged that some model inputs were considered as time invariant, which could have affected the results of the analysis.
Validity of estimate of measure of benefit The summary benefit measure was appropriate as it reflected the impact of the interventions on patient health. Discounting does not appear to have been applied. Quality of life issues were not investigated. Survival can be compared with the benefits of other health care programmes.
Validity of estimate of costs The authors did not explicitly state which perspective was adopted in the study. Only the direct costs were included in the analysis. The costs were estimated from hospital charges, which may not have been good proxies for true costs. The unit costs were presented separately from the quantities of resources used, which will allow the study to be replicated in other contexts. The costs were treated deterministically and were specific to the study setting. No discounting was explicitly applied, although it would have been relevant given the long timeframe of the analysis. The price year was not reported, which will hinder reflation exercises in other settings.
Other issues The authors stated that their estimation of the cost-effectiveness ratio was considerably lower than that reported in other studies, but this was presumably due, not only to the exclusion of some costs, but also to the approach used to calculate survival. The issue of the generalisability of the study results to other settings was not addressed and sensitivity analyses were not carried out. Therefore, the external validity of the analysis was low. The study referred to the general population aged 50 to 70 years and this was reflected in the authors' conclusions.
Implications of the study The authors suggested that further research should identify the key parameters that affect the estimation of both costs and survival.
Bibliographic details Wong S S, Leong A P, Leong T Y. Cost-effectiveness analysis of colorectal cancer screening strategies in Singapore: a dynamic decision analytic approach. In: Fieschi M, Coiera E, Li Y J (eds). MEDINFO 2004: Proceedings of the 11th World Congress on Medical Informatics. Amsterdam, The Netherlands: Amsterdam IOS Press. 2004 Other publications of related interest Lun KC. Mortality analyses of the 1990 Singapore population: I. General life tables. Annal Acad Med Singapore 1995;24:382-92.
Indexing Status Subject indexing assigned by CRD MeSH Aged; Colonoscopy; Colorectal Neoplasms /diagnosis; Cost-Benefit Analysis; Mass Screening /methods /economics; Models, Economic; Occult Blood; Sensitivity and Specificity; Sigmoidoscopy; Singapore AccessionNumber 22005008071 Date bibliographic record published 31/03/2005 Date abstract record published 31/03/2005 |
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