The Role of Price, Sociodemographic Factors, and Health in the Demand for Bariatric Surgery

, , ,
The American Journal of Managed Care, October 2005, Volume 11, Issue 10

Objectives: To estimate the effect of price, sociodemographicfactors, and health on the demand for bariatric surgery among eligibleindividuals with private health insurance, in order to enablepolicy makers and insurers to make more informed decisions concerningaccess to care for bariatric surgery.

Study Design: We conducted an Internet-based contingent valuationsurvey of 1802 obese persons eligible for bariatric surgerybut who had not undergone the procedure.

Methods: We used multivariate regression analysis to separatelyestimate the likelihood of having gastric bypass and gastric bandingsurgery at different out-of-pocket costs. We combined the resultswith estimates of the privately insured bariatric surgery-eligiblepopulation from the National Health and Nutrition ExaminationSurvey, 1999-2002, to estimate aggregate demand.

Results: Out-of-pocket cost was negatively and highly significantlyrelated to the self-reported likelihood of having surgery.Persons with higher incomes and younger persons also reported asignificantly higher likelihood of surgery. No effect was found forbody mass index or for most comorbidities. We estimate that about150 000 bariatric operations per year would be demanded by thosewith private health insurance at an out-of-pocket cost of $25 000.At $5000, we estimate a demand of 250 000 bariatric operationsper year.

Conclusions: Price is significantly and negatively related to thedemand for bariatric surgery. At an out-of-pocket cost of $5000,about 2.2% of the bariatric surgery-eligible population wouldstrongly consider surgery.

(Am J Manag Care. 2005;11:630-637)

The number of individuals receiving surgical treatmentfor obesity, also referred to as bariatric surgery,has increased dramatically in recent years.The most common form of bariatric surgery is gastricbypass, which restricts the stomach to a small pouch,thereby limiting food intake and inducing partial malabsorption.1,2 Less common but growing in popularity isgastric banding, which restricts the stomach through theuse of an adjustable band.1,2 In 1999, fewer than 30 000bariatric surgery procedures were performed in theUnited States. By 2003, this number climbed to morethan 100 000. The number of bariatric surgery procedureswas expected to approach 200 000 in 2004; however,the decision by several large private insurancecompanies and many self-insured firms to discontinuecoverage led to a slower than expected increase indemand, so the actual number of surgical procedureslikely fell short of this estimate.3 Regardless, given thatroughly 9% of US adults with private insurance are eligiblefor bariatric surgery based on National Institutes ofHealth guidelines and the National Health and NutritionExamination Survey [NHANES], 1999-2002, the potentialexists for a much greater demand in the future.

The prospect of a large increase in demand for thesurgery and the potential effect on costs and premiumswere primary motivators for many insurers to discontinuecoverage. For example, even though CIGNAHealthCare representatives acknowledged the benefitsof bariatric surgery for obese patients, the firm nolonger covers the surgery under its standard insuranceplans, citing the high cost and growing demand for surgery.4 In 2005, Aetna Inc followed suit.3,5

Specifically excluding bariatric surgery as a coveredbenefit is one of several options available to insurers.However, this option limits the ability of plan membersto get access to a procedure that has been shown to havesubstantial health benefits.5,6 Moreover, these healthbenefits may translate into financial benefits to theinsurer if improvements in health result in reductions infuture medical expenditures. Another option for insurersis to set copayment rates at levels that meet the dualobjectives of allowing greater access to bariatric surgeryfor those who need it, while minimizing the financialrisk to the insurers and members of the health plans.

Determining the appropriate copayment requires,among other factors, an understanding of the expectednumber of bariatric surgery operations demanded at agiven out-of-pocket cost. In other words, insurers wouldlike to know how "popular" the surgery is likely to be ata given copayment. To address this issue, we conductedan Internet-based survey of 1802 bariatric surgery-eligibleindividuals with private health insurance toanswer the following research questions: (1) What is thepredicted demand for gastric bypass and gastric bandingsurgery at different copayments? (2) What sociodemographicfactors affect the self-reported likelihood ofundergoing gastric bypass and gastric banding? (3)What is the predicted aggregate demand for bariatricsurgery at different price levels among adults with privatehealth insurance? This information will allowinsurers and policy makers to make more informeddecisions concerning the effect of various coverageoptions on the demand for bariatric surgery.


The data for this study were derived from a sample of1802 individuals aged 18 to 64 years with private healthinsurance who participated in an Internet-based survey.The data were fielded in 2 parts, with an initial survey of322 respondents in April 2004 and a second survey of1480 respondents in December 2004. Each survey capturedinformation on sociodemographic characteristicsof respondents and included questions concerning willingnessto pay for gastric bypass and gastric bandingsurgery. Respondents to the surveys were randomlyselected and invited to participate from national panelsmaintained by Harris Interactive, Rochester, NY (thefirst survey), and Greenfield Online, Wilton, Conn (thesecond survey). Invitations to participate in both surveyswere extended to selected participants in eachfirm's existing panels, and a brief screener was used toidentify respondents who met general eligibility guidelinesfor bariatric surgery, including a body mass index(BMI) (calculated as weight in kilograms divided by thesquare of height in meters) of 40.0 or higher, or a BMI of35.0 to 39.9 with selected comorbidities (Table 1). Bothsurvey designs included minimum quotas for sex, age,and racial or ethnic groups to ensure that the voluntaryresponses yielded a sample similar to that of the 1999-2002 NHANES. Anyone who reported having had priorbariatric surgery was excluded. Respondents who completedthe surveys were offered nominal compensationby the survey firms. This study was granted an exemptionby the institutional review board of RTIInternational.


The demand for goods and services as a function ofthe market price is often estimated using actual transactionsdata. With respect to bariatric surgery, however,this "revealed preference" approach is problematic forseveral reasons. First, because of health insurance, theactual price faced by many individuals is likely to bemuch less than the market price. Because informationon out-of-pocket costs for those who have had bariatricsurgery operations is largely unavailable, it would not bepossible to estimate demand using existing data.Second, because of government restrictions (eg, gastricbanding was not approved in the United States until2001), limitations by private payers, and a lack ofskilled providers who perform the surgery, price maynot be the primary mechanism rationing demand.Third, changing technology and an increasing relianceon centers of excellence have improved the outcomesand will likely affect the potential demand for bariatricsurgery in the future. Therefore, we chose to estimatethe demand using contingent valuation (CV) techniques.

Contingent valuation is commonly performed tomeasure willingness to pay for nonmarket goods andhas long been used in applications such as environmentaleconomics. More recently, CV has been applied tohealthcare, and it is well suited to the unique features ofthe market for bariatric surgery already mentioned.7Contingent valuation methods typically rely on surveysof potential consumers. For this analysis, potentialconsumers consisted of the panels of surgery-eligiblerespondents who had not previously undergonebariatric surgery. Respondents were asked to assesstheir likelihood of undergoing gastric bypass and gastricbanding surgery at various out-of-pocket costs. Allrespondents were shown a brief "concept board" (availableas an appendix from the author) that describedeach surgical procedure and typical outcomes and risks.When answering each valuation question, respondentshad an option to refer back to the concept board screenat any point. The survey then asked respondents the followingquestions: "Suppose you had to pay [amount]out of your own pocket for gastric bypass surgery. If thiswere the case, how likely would you be to have this procedurein the next 5 years?" Amounts were "full coverage"(which we treated as $0), $2500, $5000, $10 000,$15 000, $20 000, and $25 000. Identical questionswere asked for gastric banding surgery. For each of theamounts, 11 possible likelihood responses were given,comprising 0% to 90% in 10% increments and 99%. Theorder of questioning about gastric bypass or about gastricbanding was randomized for each participant;amounts were proposed beginning with full coverageand then in descending order from $25 000 to $2500.We converted the response to 1 (yes) if the reportedprobability was 80% or greater and to 0 (no) otherwise.We used 80% as a cutoff because prior studies8,9 foundthat this cutoff best predicts actual behavior. To estimatethe effect of price and sociodemographic factorson the self-reported likelihood of bariatric surgery, weran multivariate regressions with these factors as independentvariables and with the binary likelihood generatedfor each of the survey responses as the dependentvariable. Coefficient estimates of regressions on thecontinuous variables of 0% to 99% likelihood of undergoinggastric bypass and gastric banding were comparablein statistical significance and magnitude to theregression output given in Table 2 (results of theseregressions are available from the author).

We ran separate regressions for gastric bypass andgastric banding. The primary independent variable usedin the regressions included the hypothetical prices; toaccount for nonlinearities in demand (an increasing or adecreasing price effect), we also included the pricesquared and the price cubed. Other variables includedindicators for different BMI categories (35.0-39.9, 45.0-49.9, and &#8805;50.0, with 40.0-44.9 as the omitted referencegroup) and separate indicators for 5 significant comorbidities(coronary heart disease [CHD] or congestiveheart failure [CHF], depression, type 2 diabetes mellitus,osteoarthritis or joint pain, and sleep apnea). We alsoincluded a dummy variable indicating if the respondenthad a college degree or higher and categoricalindicators for household income (<$25 000, $25 000-$49 999, $50 000-$74 999, $75 000-$99 999, and &#8805;$100 000). Demographic indicators were age categories(18-24, 25-34, 45-54, and 55-64 years [with 35-44years as the omitted reference group]), sex, and racial orethnic dummy variables (non-Hispanic blacks,Hispanics, and other races or ethnicities [with non-Hispanic whites as the omitted reference group]).Because each respondent generated 7 observations (1for each price level), we estimated the model using apanel data random-effects regression that accounted forclustering of questions within individuals. We also useda fixed-effects regression, but the price coefficients wereclose to those in the random-effects regression. Becauseour dependent variable was binary, we also used logisticregressions. Panel data logistic regressions with randomand fixed effects generated significance and marginaleffects comparable to those summarized in Table 2.However, when generating predictions, we found thatthe logistic regression results did not fit the data as wellas those from the random-effects regression (results areavailable from the author).

Last, using information on the number of privatelyinsured individuals eligible for bariatric surgery, wegenerated an aggregate demand curve that includedthe predicted demand for both gastric bypass and gastricbanding. Because the procedures are substitutes,we could not simply sum the demand for each procedureat a given price level. For example, some respondentsstated that at an out-of-pocket cost of $2500they would be 99% likely to undergo both proceduresin the next 5 years. To account for this impossibility,we assumed that each participant could get at most 1procedure and estimated the aggregate demand forbariatric surgery by using the minimum ofthe self-reported likelihoods for gastricbypass and for gastric banding. Thisapproach provides a conservative estimateof the aggregate demand for bariatric surgeryoverall. Using the minimum, we thenreestimated the regression and used theresults to predict probabilities of bariatricsurgery at a range of out-of-pocket costsbetween $0 (full coverage) and $25 000.We then multiplied the results by the estimatednumber of privately insured personsaged 18 to 64 years eligible for surgery(10.9 million), calculated from the 1999-2002 NHANES, to estimate the aggregatedemand for bariatric surgery during thenext 5 years. We then divided the predictionsby 5 to generate an estimated annualdemand for bariatric surgery operations.


Table 1 gives summary statistics of thesurvey participants. Slightly less than onethird of the sample were aged 35 to 44years, 28.5% were 45 to 54 years, and 19.7%were 25 to 34 years. Seventy-two percent ofrespondents were non-Hispanic whites,11.3% were non-Hispanic blacks, and 13.9%were Hispanics. Overall, 40.1% of respondentswere male. Compared with the generalpopulation, the sample was highlyeducated. Almost 85% of respondentsreported having some schooling beyond ahigh school degree or general equivalencydiploma. This is likely an artifact of theInternet-based survey and the restriction toindividuals with private health insurance,because persons with private health insuranceare more likely to be employed in jobspaying more and requiring higher educationlevels. Consistent with higher educationlevels, household incomes were alsohigher than in the general population.Twenty-four percent of respondentsreported household incomes between$50 000 and $74 999, and 33.7% reportedhousehold incomes of $75 000 or greater. The meanBMI of participants was 42.2, with almost 45% of thesample being eligible for bariatric surgery by having aBMI of 35.0 to 39.9 and 1 or more comorbidities. Ofthe 5 major comorbidities listed in Table 1, the mostcommon was depression (31.7%), followed byosteoarthritis or joint pain (29.4%) and type 2 diabetesmellitus and sleep apnea (21.3% each).

Figure 1 shows the proportions of men and womenwho reported an 80% or greater likelihood of bariatricsurgery within the next 5 years at each of the 7 price levels.At full coverage, 25.8% and 29.9% of men and womenreported being 80% or more likely to undergo gastricbypass and gastric banding, respectively, in the next 5years. At an out-of-pocket cost of $25 000, these self-reportedlikelihoods dropped to 10.9% and 11.4% for gastricbypass and gastric banding, respectively. Men andwomen indicated a slightly lower likelihood of undergoinggastric bypass compared with gastric banding,although the difference between the 2 procedures wassmall and narrowed as the out-of-pocket cost increased.Men reported a slightly greater likelihood of undergoingeither procedure. Consistent with economic theory, theself-reported likelihood of surgerydecreased with increases in theout-of-pocket cost.







Results of the panel data random-effects regressions for gastricbypass and gastric banding aregiven in Table 2. As expected, theprice variables (price and pricesquared) were highly significantfor both procedures (< .001 and= .004, respectively, for gastricbypass and < .001 and = .006,respectively, for gastric banding),suggesting that out-of-pocketcost is indeed a major driver ofinterest in surgery. We also foundsignificant income effects forgastric banding. Individualsfrom households with annualincomes of $75 000 to $99 999and of $100 000 and higherreported greater likelihoods ofgastric banding in the next 5years that were 3.4 (= .046)and 4.3 (= .03) percentagepoints higher, respectively, relativeto the omitted reference group($50 000-$74 999). Estimates forgastric bypass were similar butwere not significant at conventionallevels.






The results also reveal thatindividuals aged 45 to 64 yearsreported a much lower likelihoodof undergoing gastric bypass surgery,namely, 4 percentage pointsless likely among those aged 45 to54 years (= .006) and 5 percentagepoints less likely amongthose aged 55 to 64 years (=.003), relative to the omitted reference group (35-44years). None of the age terms was significant for gastricbanding. We also found no statistically significant differencesby education level. Consistent with the data shownin Figure 1, men reported a 3-percentage-point greaterlikelihood than women of undergoing gastric bypass(= .005). Non-Hispanic blacks reported 4-percentage-point (= .01) and 7-percentage-point (<.001) lower likelihoods of gastric bypass and gastricbanding surgery, respectively. Self-reported likelihoodsfor other racial or ethnic groups were not statisticallydifferent from those of non-Hispanic whites, theomitted reference group.



Of the 5 included comorbidities,we found a significantlylower self-reportedlikelihood of undergoing gastricbanding (6.6%, = .002)for persons with CHD or CHF;the 4-percentage-point lowerlikelihood of undergoing gastricbypass associated withhaving CHD or CHF was notsignificant (= .10). Thislower self-reported likelihoodmay reflect the notion thatindividuals with CHD or CHFare ineligible for surgery.Surprisingly, none of the medicalconditions that bariatricsurgery has been shown toimprove, such as depression,type 2 diabetes mellitus, osteoarthritis or joint pain, andsleep apnea, significantly affected the self-reported likelihoodof having the surgery.5 Body mass index was alsonot a significant predictor.

The estimated aggregate demand curve is shown inFigure 2. We estimate that, at an out-of-pocket cost of$25 000, about 150 000 surgical operations per yearwould be demanded by individuals with private healthinsurance. This price is approximately equal to the fullcost of gastric bypass surgery.4 The figure also showsthat decreasing the out-of-pocket cost from $25 000 to$10 000 results in only a small increase in the totalnumber of procedures demanded. At prices lower than$10 000, demand is more responsive to changes inprice. However, the results suggest that, even when fullycovered by insurance, demand among those with privateinsurance would not exceed about 375 000 proceduresper year, about double the current number.


These analyses generated several important findings.At any given out-of-pocket cost, the number of individualswho reported being likely to undergo surgery forgastric banding surgery was greater than that for gastricbypass surgery. To date, the number of gastric bandingprocedures performed in the United States is much lessthan the number of gastric bypass operations performed.10 This apparent contradiction may be explainedby different coverage rates between the 2 procedures.Although gastric banding has been available in Europefor several years, it was only approved in the UnitedStates in 2001, and many insurers have opted not tocover it. Therefore, although the actual price of gastricbanding (approximately $17 000) is less than the$25 000 price tag for gastric bypass surgery, the out-of-pocketcost to date is likely to have been much less forgastric bypass. However, as insurers increasingly optnot to cover either surgery, these results suggest thatthe demand for gastric banding surgery is likely toincrease at the expense of the demand for gastric bypasssurgery.

The higher demand for gastric banding may seemsurprising given that the published literature suggeststhat gastric bypass surgery has much greater effectiveness.5,11 However, gastric bypass surgery is generally notreversible. It is possible that individuals are willing totrade off some of the potential benefits for a fullyreversible procedure.

Although we found a strong and statistically significanteffect of price on the self-reported likelihood ofundergoing bariatric surgery, few other factorsappeared to significantly affect the demand. In fact,neither a higher BMI nor an increase in the number ofobesity-related comorbidities appeared to affect theself-reported likelihood of undergoing the surgery.From an insurer's perspective, this finding may be concerning.Insurers that offer coverage for bariatric surgerymight want to target the surgery to that subset ofthe morbidly obese population that has the most togain (ie, those with BMIs in the higher range or thosewith certain comorbidities) to avoid what they mayperceive as adverse selection. This finding suggests thatmore stringent eligibility criteria may be necessary toachieve this outcome.

As noted in the introduction, close to 200 000bariatric surgery procedures were expected to be per-formed in 2004. The aggregate demand curve shown inFigure 2 would predict this quantity at a mean out-of-pocketcost of roughly $7500. Given that many insuredindividuals likely paid significantly less, while otherspaid the full cost, this estimate does not seem out ofstep with current data.

The aggregate demand curve can be used to predictthe effects of the discontinuation of coverage forbariatric surgery. At a mean cost of $20 000 and noinsurance coverage, the demand for bariatric surgery(gastric bypass or gastric banding) would be roughly160 000 procedures per year. Without insurance coverage,the aggregate demand curve suggests that modestdecreases in the price of surgery, perhaps throughchanges in technology or increases in the number ofphysicians who perform the surgery, are unlikely tohave a significant effect on demand. We estimate thatroughly 150 000 operations would be demanded at anout-of-pocket cost of $25 000, whereas this figureclimbs to only 175 000 when the price falls to $10 000.In other words, the demand for surgery is very inelasticat this end of the curve.

In fact, the aggregate demand curve remains inelasticeven at lower prices. For example, at $2500 we estimatethat roughly 300 000 bariatric operations wouldbe demanded. Doubling the price to $5000, whichequates to a 20% copayment at a $25 000 price of gastricbypass surgery, only reduces the total quantitydemanded by 19%. A further increase to $7500 reducesthe total quantity demanded by about 35%.

Given that 1 of 3 adults in the United States isobese, the demand for bariatric surgery may not be aslarge as some have hypothesized. Based on data fromthe 1999-2002 NHANES, we estimate that roughly 11million individuals with private insurance in theUnited States are eligible for bariatric surgery. At anout-of-pocket cost of $5000, about 250 000 bariatricsurgery operations would be demanded each year, orapproximately 2.2% of the eligible population. Aninsurance company with 100 000 adult members anda 9% prevalence of surgery-eligible obesity would likelyprovide coverage for about 200 bariatric surgeryoperations each year. Moreover, a modest copaymenthas the additional benefit of lowering the cost of coveringthe surgery, while simultaneously increasingaccess to those who need it most.

Our analysis has several limitations. Perhaps the primarylimitation is that our sample may not be representativeof the privately insured population eligible forbariatric surgery. As a check, we compared our samplewith a nationally representative sample of privatelyinsured, surgery-eligible individuals (based on as closeto the same definition of eligibility as possible) whoparticipated in the 1999-2002 NHANES (results areavailable from the author). Sixty percent of our samplewere aged 35 to 54 years vs 57.6% of the NHANES sample.Men made up 40.1% of our sample vs 38.0% of theNHANES sample, and both populations were roughly72% non-Hispanic white. The mean BMI in our samplewas 42.2 vs 40.9 in the NHANES sample, and the prevalencesof CHD or CHF and type 2 diabetes mellituswere also nearly identical. However, we found 2 differencesthat may affect our results. A larger number ofparticipants in our sample had more than a high schooleducation (84.1% vs 56.8%), and our sample had a largerpercentage of participants whose household incomewas at least $50 000 per year (57.8% vs 46.4%). Both ofthese features are likely attributable to the online surveysample after survey. Because our results show thatgreater income is positively associated with thedemand for bariatric surgery, it is possible that accessto a more representative sample would have led tosmaller estimates of aggregate demand.

Although CV methods are well established, they arenot without criticism.12 One concern is that it is difficultfor people to fully value a procedure before theyexperience it, even when shown the detailed informationabout each procedure that we provided in the conceptboards. Our sample likely includes individualswith varying degrees of prior information about the 2types of surgery, which may differentially affect theirvaluations. Moreover, although the information containedin the concept boards was accurate to the bestof our knowledge, it is possible that the way the informationwas presented may have affected the responses.Another criticism concerns the 80% cutoff to predictwho does or does not get the surgery at a given pricelevel. Additional analyses (available from the author)using cutoffs of 70% and 90% resulted in parallel shiftsof the aggregate demand curve (higher or lower predictedquantities at each price) but did not change theprimary conclusions concerning the relationshipbetween changes in price levels or in sociodemographiccharacteristics on the demand for the surgery.Moreover, the predicted number of surgical proceduresbased on the 80% cutoff appears to be in the range ofthe number of bariatric procedures that were performedin 2004.

Our results are limited to subjects with privatehealth insurance and do not reflect the uninsured ormembers of public insurance programs. Inclusion ofthese populations would suggest that the aggregatedemand for the surgery would be greater than what isreported herein. Our estimates also reflect current populations.If the size of the surgery-eligible populationcontinues to grow at current rates, the aggregatedemand for the surgery will also increase. Changes intechnology that improve the effectiveness of bariatricsurgery might increase demand, whereas changes intechnology for substitute products, such as the introductionof effective weight loss medications, might substantiallyreduce the demand.10 Finally, we acknowledgethat clinical guidelines and medical necessity oftendrive coverage decisions and that demand considerationsmay be of secondary importance. Regardless,these estimates provide previously unavailable informationthat should assist insurers and policy makers inappropriate coverage strategies for bariatric surgery.

From RTI International, Research Triangle Park, NC (EAF, DSB); Ethicon Endo-Surgery,Inc, Cincinnati, Ohio (YA); and Copernicus Marketing Consulting, Waltham, Mass (AHT).

This study was sponsored by Ethicon Endo-Surgery, Inc. The data were collected byCopernicus Marketing Consulting for Ethicon Endo-Surgery, Inc. All analyses and datareporting were conducted by researchers at RTI International, who had final right ofapproval of publication of this article.

Address correspondence to: Eric A. Finkelstein, PhD, RTI International, 3040 CornwallisRoad, PO Box 12194, Research Triangle Park, NC 27709-2194. E-mail:

Obes Res.

1. Lehman Center Weight Loss Surgery Expert Panel. Commonwealth ofMassachusetts Betsy Lehman Center for Patient Safety and Medical Error ReductionExpert Panel on Weight Loss Surgery: executive report. 2005;13:205-226.

Surg Endosc.

2. Jones DB, Provost DA, DeMaria EJ, et al. Optimal management of the morbidlyobese patient: SAGES appropriateness conference statement. 2004;18:1029-1037.

3. Aon Corporation. Bariatric surgery policy guidance. Available at: Accessed March 8, 2005.

Orlando Sentinel.

4. Wessel H. For workers, it could be a big loss: insurance companies are eitherdropping coverage for weight-loss surgery or making companies pay more to covertheir employees. September 8, 2004:G1.


5. Buchwald H, Avidor Y, Braunwald E, et al. Bariatric surgery: a systematicreview and meta-analysis. 2004;292:1724-1737.

Ann Surg.

6. Christou NV, Sampalis JS, Liberman M, et al. Surgery decreases long-term mortality,morbidity, and health care use in morbidly obese patients. 2004;240:416-424.

J Health Econ.

7. Mataria A, Donaldson C, Luchini S, Moatti JP. A stated preference approach toassessing health care-quality improvements in Palestine: from theoretical validity topolicy implications. 2004;23:1285-1311.

Environ Resour Econ.

8. Champ PA, Bishop RC. Donation payment mechanisms and contingent valuation:an empirical study of hypothetical bias. 2001;19:383-402.

Environ Resour Econ.

9. Poe GL, Clark JE, Rondeau D, Schulze WD. Provision point mechanisms andfield validity tests of contingent valuation. 2002;23:105-131.

Surg Endosc.

10. Trus TL, Pope GD, Finlayson SR. National trends in utilization and outcomesof bariatric surgery. 2005;19:616-620.

Ann Surg.

11. Weber M, Muller MK, Bucher T, et al. Laparoscopic gastric bypass is superiorto laparoscopic gastric banding for treatment of morbid obesity. 2004;204:975-983.

J Econ Perspect.

12. Diamond P, Hausman J. Contingent valuation: is some number better than nonumber? 1994;8:45-64.