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The cost-effectiveness of the WINGS intervention: a program to prevent HIV and sexually transmitted diseases among high-risk urban women |
Chesson H W, Greenberg J B, Hennessy M |
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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 The health intervention examined was the Women in Group Support (WINGS) project for urban heterosexual women at risk of acquiring human immunodeficiency virus (HIV) and other sexually transmitted diseases (STDs). This was a 6-session group-based intervention offering training in condom use (appropriate use of condoms) and in communication skills (such as talking to sexual partners about condom usage).
Economic study type Cost-effectiveness analysis and cost-utility analysis.
Study population The study population comprised urban heterosexual women at risk of acquiring HIV and other STDs.
Setting The setting was the community. The economic study was carried out in the USA.
Dates to which data relate The effectiveness data were derived from studies published between 1994 and 2000. Data on resource consumption and costs were gathered in 1996 and from studies published between 1996 and 2000. The price year was 1996.
Source of effectiveness data The effectiveness evidence came from published studies and the authors' assumptions.
Modelling A structured equation model was used to evaluate the effectiveness of the intervention programme. A simplified version of the model was reported in the paper, while the calculations necessary to calculate the effectiveness were reported in an appendix. The model was based on a published study (Greenberg et al., see Other Publications of Related Interest).
Outcomes assessed in the review The outcomes assessed from the published studies were:
the probabilities of condom use without participation in the intervention, with participation in the full intervention, and with participation in the CUSC;
the annual probability of HIV infection without participation in the intervention;
condom effectiveness;
the number of women in the intervention;
the duration of the intervention effect; and
the number of quality-adjusted life-years (QALYs) saved per HIV infection averted.
Study designs and other criteria for inclusion in the review One of the primary studies was the WINGS trial (see Other Publications of Related Interest). This involved 602 women from May 1995 through July 1997, who were randomly assigned to the intervention or control groups. No details on the other studies were reported.
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 effectiveness evidence used in the model was derived from nine primary studies.
Methods of combining primary studies Investigation of differences between primary studies Results of the review The probability values were 53.2% for condom use without participation in the intervention, 57.7% (range: 55.45 - 59.95) for condom use with participation in the full intervention, and 56.8% (range: 55 - 58.6) for condom use with participation in the CUSC.
The annual probability of HIV infection without participation in the intervention was 0.019 (range: 0.0095 - 0.029).
The condom effectiveness was 95% (range: 85 - 98).
The number of women in the intervention was 266.
The duration of the intervention effect was 6 months (range: 3 - 9).
The number of QALYs saved was 11.23 (range: 9.34 - 13.18) per HIV infection averted.
Methods used to derive estimates of effectiveness The authors made some assumptions to augment data used in the decision model.
Estimates of effectiveness and key assumptions The main assumption used in the analysis was that the benefits of the interventions (averted HIV infections) accrued in the 6 months following the intervention.
Measure of benefits used in the economic analysis The benefit measures used in the economic analysis were the number of expected HIV cases averted and the number of QALYs saved per infection averted. The QALYs were obtained from published studies. The HIV cases averted were calculated using the decision model, and a model-based evaluation that suggested a linear relationship between increased condom usage and HIV risk reduction.
Direct costs A 3% discount rate was used since the costs were estimated over more than two years. The unit costs were reported separately from the quantities of resources used. The health service costs used in the economic evaluation were for facility rent, facilitator salary and benefits, facilitator training, recruitment, incentive payments, client transportation and meals, senior staff time for quality assurance, course materials and child care. The cost/resource boundary adopted in the study was that of the society. Direct costs were included from the perspective of the payer for the WINGS project. The costs and quantities were estimated on the basis of the WINGS trial and data derived from a published study (Holtgrave and Kelly, 1996). The direct costs per HIV case were derived from a further published study (Holtgrave and Pinkerton, 1997). Some assumptions were also made and reported. The costs were reported in 1996 prices.
Statistical analysis of costs The costs were treated deterministically.
Indirect Costs The indirect costs, such as productivity losses, were included in the analysis because a societal perspective was adopted. The unit costs were reported separately from the quantities of resources used. The indirect costs were taken into account through childcare compensation, travel compensation and incentive payments, as in the case of direct costs. The indirect costs were estimated from two published studies (Mullins et al., 2000; Holtgrave and Pinkerton, 1997) and data collected during the WINGS trial. A 3% discount rate was used and the prices were reported in 1996 values.
Sensitivity analysis Univariate and multivariate sensitivity analyses were conducted to evaluate the robustness of the estimated cost per HIV infection averted and QALYs gained to variations in several variables. For example, the cost of the intervention, the effectiveness of the intervention, the annual probability of acquiring HIV, the duration of the effectiveness of the intervention, and the cost per case of HIV. The ranges used in the analysis were plus or minus 50% of the values used in the base-case. A Monte Carlo simulation (20,000 distributions) was also performed.
Estimated benefits used in the economic analysis The number of HIV cases averted was 0.2195 with the complete intervention and 0.1756 with the CUSC. The QALYs were not reported separately, but were combined in the synthesis of the costs and benefits.
Cost results The cost was $121,296 with the complete intervention and $51,338 with the CUSC.
The HIV costs averted were $73,960 with the complete intervention and $59,168 with the CUSC when the indirect HIV costs were included. When the indirect HIV costs were excluded, these costs were $42,796 (complete) and $34,237 (CUSC), respectively. Consequently, the net costs (intervention costs minus HIV costs averted) were $47,336 with the complete intervention and -$7,830 with the CUSC when the indirect HIV costs were included, and $78,500 (complete) and $17,101 (CUSC) when they were excluded.
Synthesis of costs and benefits Incremental cost-effectiveness and cost-utility ratios were calculated to combine the costs and benefits of the two strategies. The indirect costs were not included in the cost-utility analysis so as to avoid double counting.
Compared with no intervention (which had no programme cost and resulted in 2.54 new HIV infections), the incremental cost per HIV case averted was $215,690 with the complete intervention and a negative value (cost-saving) with the CUSC when the indirect HIV costs were included. When the indirect HIV costs were excluded, these costs were $357,690 (complete) and $97,404 (CUSC), respectively.
Compared with the CUSC, the incremental cost per HIV case averted with the complete intervention was $1,256,831 when the indirect HIV costs were included and $1,398,831 when they were excluded.
Compared with no intervention, the incremental cost per QALY was $31,851 with the complete intervention and $8,674 with the CUSC.
The incremental cost per QALY with the complete intervention over the CUSC was $124,562.
The one-way sensitivity analyses showed that the study results were quite sensitive to variations in the annual probability of acquiring HIV, the effectiveness and cost of the intervention, and the duration of the intervention's effect on condom usage.
In the multivariate sensitivity analyses, the cost per HIV averted ranged from cost-saving values to $1,552,430 with the complete intervention and from cost-saving values to $660,175 with the CUSC, when the indirect costs were included. When the indirect costs were excluded, they ranged from $27,506 to $1,635,740 with the complete intervention and from cost-saving values to $783,820 with the CUSC. The lower and upper bounds reported represented the 5th and 95th percentiles of the cost-effectiveness ratios generated in the Monte Carlo simulations.
Authors' conclusions The human immunodeficiency virus (HIV) prevention programme, in particularly the condom use skills component (CUSC), was below the critical threshold of $50,000 per quality-adjusted life-year (QALY) gained when the indirect costs were not included, compared with no intervention. Under some scenarios, the interventions both led to cost-savings. However, the incremental cost per QALY of the complete intervention relative to the CUSC was far higher than the threshold. The inclusion of the indirect costs and the use of HIV cases averted led to quite high cost-effectiveness ratios.
CRD COMMENTARY - Selection of comparators The rationale for the choice of the comparator was clear. No intervention was selected since no prevention programmes for HIV or other STDs were routinely implemented at the time of the study. You should decide whether it represents a valid comparator in your own setting.
Validity of estimate of measure of effectiveness The analysis of effectiveness used data derived from published studies, but a formal review of the literature was not undertaken. No search method was reported and details of the primary studies were only reported for the WINGS trial. Primary study estimates appear to have been combined using narrative methods. It was unclear whether the authors considered any differences across the primary studies when estimating the effectiveness. The authors also made some assumptions to derive outcome data.
Validity of estimate of measure of benefit QALYs and HIV cases averted were used as the benefit measures in the economic analysis. The QALYs were derived from published studies and sensitivity analyses were conducted to investigate uncertainty around this estimation. Details of the utility values used were not reported. HIV cases averted were calculated using a published analytic model. The use of QALYs enables the benefits of the HIV prevention programme to be compared with those of other prevention interventions implemented in the health care system.
Validity of estimate of costs The perspective adopted in the study was explicitly reported. It appears that all the relevant categories of cost have been included in the analysis. The indirect costs were calculated using childcare compensation, travel compensation and incentive payments. The unit costs were reported separately from the quantities of resources used and the price year was reported. These factors enhance the reproducibility of the study results in other contexts. The source of the cost data was stated, while some assumptions were made to estimate resource consumption. The costs were treated deterministically in the base-case, but sensitivity analyses were performed on key cost factors.
Other issues The authors compared their findings with those from published studies, but did not address the issue of the generalisability of the study results to other settings. Sensitivity analyses were performed and the results were reported in detail. Thus, the external validity of the analysis was enhanced. The study referred to women at risk of HIV and this was reflected in the conclusions of the analysis. The authors commented some limitations of their analysis:
there was uncertainty around the effectiveness of the intervention in significantly increasing condom usage in comparison with no intervention;
the CUSC was considered to be separate, but in reality it was not offered as an independent intervention;
the number of HIV infections averted was calculated on the basis of assumptions and a statistical model, thus some imprecision may exist; and
the cost information was retrospectively collected.
When combining the costs and QALYs the authors did not include the indirect costs due to possible double counting. There is some controversy in the literature about this issue.
Implications of the study As reported in other analyses, it appears more cost-effective to implement a cheaper programme (such as the CUSC) for a larger number of women than a more intensive and expensive programme (such as the complete intervention) for a reduced number of patients. The inclusion of the HIV prevention programme into existing programmes for high-risk women would further improve the cost-effectiveness of the intervention, by reducing its costs. The analysis may have underestimated the true benefits of the intervention because it did not consider the reduction of HIV infection among the women's sexual partners, and the minor rate of infections with other STDs and unintended pregnancies.
Bibliographic details Chesson H W, Greenberg J B, Hennessy M. The cost-effectiveness of the WINGS intervention: a program to prevent HIV and sexually transmitted diseases among high-risk urban women. BMC Infectious Diseases 2002; 2(1): 24 Other publications of related interest Greenberg J, Hennessy M, MacGowan R, Celantano D, Gonzales V, Van Devanter N, et al. Modeling intervention efficacy for high-risk women - The WINGS Project. Evaluation and the Health Professions 2000;23:123-48.
Holtgrave DR , Kelly JA. Preventing HIV/AIDS among high-risk urban women: the cost-effectiveness of a behavioural group intervention. American Journal of Public Health 1996;86:1442-5.
Holtgrave DR, Pinkerton SD. Updates of cost of illness and quality of life estimates for use in economic evaluations of HIV prevention programs. Journal of Acquired Immune Deficiency Syndromes and Human Retrovirology 1997;16:54-62.
Mullins CD, Whitelaw G, Cooke JL, Beck EJ. Indirect cost of HIV infection in England. Clinical Therapeutics 2000;22:1333-45.
Indexing Status Subject indexing assigned by NLM MeSH Cost-Benefit Analysis; Female; HIV Infections /economics /prevention & Humans; Preventive Health Services /economics; Sexually Transmitted Diseases /economics /prevention & Urban Health; Urban Population; Women's Health; control; control AccessionNumber 22003006090 Date bibliographic record published 30/11/2003 Date abstract record published 30/11/2003 |
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