in response to payers , purchasers , patients , and professional organizations , public reporting of healthcare outcomes has seen a rapid increase over the past decade . despite early successful initiatives in cardiac surgery in 1990s , hospital compare is a public reporting program operated by the centers for medicare and medicaid services ( cms ) which reports process - of - care , patient satisfaction , and outcome measure performance for more than 4000 medicare - certified hospitals in the united states . currently , some postoperative complications are publicly reported , but these are based on administrative data and have been shown to be relatively inaccurate . the american college of surgeons national surgery quality improvement program ( acs nsqip ) is a quality assessment and improvement program in which clinical data are used to provide hospitals with risk- and case - mix adjusted , nationally benchmarked , 30-day postoperative outcomes . this standardized data collection and detailed risk adjustment approach offers hospital quality comparisons that are far more accurate than those provided by administrative data . in october 2012 , acs nsqip hospitals were offered the opportunity to voluntarily publicly report three of their acs nsqip risk - adjusted surgical outcomes on hospital compare ( cms - nsqip initiative ) . this represents the first national public reporting initiative of postoperative outcomes data based on clinical registry data . the first wave of participation in this voluntary pilot initiative began in october 2012 with a second opportunity for hospitals to join in april 2013 . our objectives were to examine differences between hospitals that chose to participate in the cms - nsqip public reporting initiative vs. those that did not by examining ( 1 ) structural characteristics ; ( 2 ) performance on publicly reported process , patient experience , and outcome measures ; and ( 3 ) performance on the three acs nsqip surgical care outcomes that each hospital could chose to publicly report on hospital compare . we hypothesized that the acs nsqip hospitals with more structural characteristics reflecting quality and better performance on publicly reported hospital compare ( process , outcome and patient experience ) measures would be more likely to participate in the cms - nsqip initiative . hospitals were given the opportunity to review their acs nsqip outcomes before deciding to publicly report them to cms . hospitals that participated in the initial reporting of acs nsqip outcomes were identified through the hospital compare october 2012 release , as were participants in the april 2013 release ( wave two ) . first , the 2010 american hospital association annual ( aha ) survey was used to ascertain hospital - level structural characteristics for each acs nsqip hospital . second , the 2010 release of the cms hospital compare dataset was used to obtain 58 measures of hospital quality : 6 risk - adjusted outcomes , 32 process - of - care measures , 10 patient experience measures ( hospital consumer assessment of healthcare providers and systems ( hcahps ) ) , and 10 agency for healthcare research quality ( ahrq ) risk - adjusted patient safety indicators ( psi ) . lastly , two consecutive waves of acs nsqip surgical outcomes of death and serious morbidity after elderly surgery , colon surgery , and lower extremity bypass were examined . using data from the aha annual survey , differences in 20 hospital characteristics were compared between cms - nsqip participants and non - participants including hospital ownership / control ( government , non - governmental non - profit , and for - profit ) , number of hospital beds ( < 200 , 200299 , 300 + ) , number of hospital admissions and inpatient surgical operations , number of operating rooms , commission on cancer accreditation , joint commission ( jc ) accreditation , and membership in the council of teaching hospitals ( coth ) . finally , two other measures related to quality of care present in the aha annual survey were included : ( 1 ) hospitals tracked and communicated clinical / health information , and ( 2 ) hospitals disseminated reports to the community on quality and cost of service . from the hospital compare dataset , 6 risk - adjusted outcome measures were examined : death and readmission related to heart attack , heart failure , and pneumonia . thirty - two process - of - care measures were examined : 11 heart attack or chest pain measures , 4 heart failure measures , 6 pneumonia process of care measures , and 11 surgical care improvement project ( scip ) process - of - care measures . finally , 10 ahrq risk - adjusted psi were compared and categorized as better - than - u.s .- national - rate , no - different - than - u.s .- national rate , and worse - than - u.s .- national rate by hospital compare . three different acs nsqip surgical measures were made available for hospitals to voluntarily publicly report : death or serious complication after : ( 1 ) elderly surgery , ( 2 ) colorectal surgery , or ( 3 ) lower extremity bypass surgery . for each hospital that reported acs nsqip measures on hospital compare , their performance was reported as  better - than - average  ,  average , worse - than - average  or  not available  if the number of cases were too small to reliably report or the hospital did not perform the measure . better  and  worse  performers was compared between public reporting participants and non - participants for both waves of data . in addition , proportions of hospitals reporting each outcome in wave two were compared to proportions of hospitals reporting each outcome in wave one . those hospitals that reported an outcome as data  not available  were not included in the comparisons for that specific outcome measure . bivariate analyses were completed using chi - squared and t - tests to compare aha hospital characteristics and hospital compare measures by cms - nsqip participation status . multivariable logistic regression models were estimated to identify the hospital characteristics associated with participation in cms - nsqip public reporting ( vs. non - participants ) including number of hospital beds , total surgical operations , jc accreditation , acs - cancer program accreditation , and coth accreditation . a second group of multivariable logistic regression models were developed to examine the association between poor performance ( defined as hospitals performing below the 25th percentile for a given hospital compare measure ) and participation in cms - nsqip public reporting . each model was adjusted for the number of hospital beds , coth membership , and type of hospital . as a final step , for both waves of data , we compared percentages of  better - than - average ,   average ,  and  worse  than - average performers for the three acs nsqip publicly reported surgical outcomes between cms - nsqip participants and the acs nsqip sample as a whole , using t - tests for two proportions . analyses were completed using sas 9.3 ( sas institute inc . , cary , nc , usa ) . as only de - identified , hospital - level secondary data were used , the northwestern university irb deemed this study exempt from human subjects research approval . hospitals were given the opportunity to review their acs nsqip outcomes before deciding to publicly report them to cms . hospitals that participated in the initial reporting of acs nsqip outcomes were identified through the hospital compare october 2012 release , as were participants in the april 2013 release ( wave two ) . first , the 2010 american hospital association annual ( aha ) survey was used to ascertain hospital - level structural characteristics for each acs nsqip hospital . second , the 2010 release of the cms hospital compare dataset was used to obtain 58 measures of hospital quality : 6 risk - adjusted outcomes , 32 process - of - care measures , 10 patient experience measures ( hospital consumer assessment of healthcare providers and systems ( hcahps ) ) , and 10 agency for healthcare research quality ( ahrq ) risk - adjusted patient safety indicators ( psi ) . lastly , two consecutive waves of acs nsqip surgical outcomes of death and serious morbidity after elderly surgery , colon surgery , and lower extremity bypass were examined . using data from the aha annual survey , differences in 20 hospital characteristics were compared between cms - nsqip participants and non - participants including hospital ownership / control ( government , non - governmental non - profit , and for - profit ) , number of hospital beds ( < 200 , 200299 , 300 + ) , number of hospital admissions and inpatient surgical operations , number of operating rooms , commission on cancer accreditation , joint commission ( jc ) accreditation , and membership in the council of teaching hospitals ( coth ) . finally , two other measures related to quality of care present in the aha annual survey were included : ( 1 ) hospitals tracked and communicated clinical / health information , and ( 2 ) hospitals disseminated reports to the community on quality and cost of service . from the hospital compare dataset , 6 risk - adjusted outcome measures were examined : death and readmission related to heart attack , heart failure , and pneumonia . thirty - two process - of - care measures were examined : 11 heart attack or chest pain measures , 4 heart failure measures , 6 pneumonia process of care measures , and 11 surgical care improvement project ( scip ) process - of - care measures . finally , 10 ahrq risk - adjusted psi were compared and categorized as better - than - u.s .- national - rate , no - different - than - u.s .- national rate , and worse - than - u.s .- national rate by hospital compare . three different acs nsqip surgical measures were made available for hospitals to voluntarily publicly report : death or serious complication after : ( 1 ) elderly surgery , ( 2 ) colorectal surgery , or ( 3 ) lower extremity bypass surgery . for each hospital that reported acs nsqip measures on hospital compare , their performance was reported as  better - than - average  ,  average ,   worse - than - average  or  not available  if the number of cases were too small to reliably report or the hospital did not perform the measure . the proportion of  better  and  worse  performers was compared between public reporting participants and non - participants for both waves of data . in addition , proportions of hospitals reporting each outcome in wave two were compared to proportions of hospitals reporting each outcome in wave one . those hospitals that reported an outcome as data  not available  were not included in the comparisons for that specific outcome measure . bivariate analyses were completed using chi - squared and t - tests to compare aha hospital characteristics and hospital compare measures by cms - nsqip participation status . multivariable logistic regression models were estimated to identify the hospital characteristics associated with participation in cms - nsqip public reporting ( vs. non - participants ) including number of hospital beds , total surgical operations , jc accreditation , acs - cancer program accreditation , and coth accreditation . a second group of multivariable logistic regression models were developed to examine the association between poor performance ( defined as hospitals performing below the 25th percentile for a given hospital compare measure ) and participation in cms - nsqip public reporting . each model was adjusted for the number of hospital beds , coth membership , and type of hospital . as a final step , for both waves of data , we compared percentages of  better - than - average ,   average ,  and  worse  than - average performers for the three acs nsqip publicly reported surgical outcomes between cms - nsqip participants and the acs nsqip sample as a whole , using t - tests for two proportions . analyses were completed using sas 9.3 ( sas institute inc . , cary , nc , usa ) . as only de - identified , hospital - level secondary data were used , the northwestern university irb deemed this study exempt from human subjects research approval . of the 452 acs nsqip hospitals included in this analysis , 17.5% participated in the cms - nsqip initiative ( n=80 ) by publicly reporting outcomes to hospital compare , even if the outcome was reported as data  not available ( i.e. , some hospitals agreed to report but did not have sufficient cases for a particular measure to qualify for public reporting ) of the 80 hospitals that participated , 73 ( 91.3% ) reported the elderly surgery outcome , 69 ( 86.3% ) reported the colon surgery outcome , and 54 ( 67.5% ) reported the lower extremity bypass outcome on hospital compare . of the 80 hospitals , 56.3% reported all three measures , 23.7% reported two of the measures , 10.0% reported just one outcome while an additional 8 hospitals ( 10% ) chose to participate in cms - nsqip even though their outcomes for all three measures were reported as  not available . overall , acs nsqip hospitals ( n=452 ) had a mean of 237 ( standard deviation ( sd ) = 157 ) general medical and surgical adult beds , 21,145 ( sd=14,806 ) annual admissions , and 6,488 ( sd=5,140 ) inpatient surgical operations ( table 1 ) . the majority were jcaho accredited ( 92.4% ) , commission on cancer accredited ( 70.8% ) , and had acgme residency training programs ( 61.3% ) and/or coth accreditation ( 34.3% ) . in addition , 89.1% reported the  dissemination of reports to the community on quality and cost of service ,  while 95.9% reported  tracking and communicating clinical health information across their organization .  in comparing cms - nsqip public reporting participants and non - participants , cms - nsqip participating hospitals had larger number of hospital beds , admissions , medicare discharges , inpatient and outpatient surgical operations , and hospital operating rooms compared to non - participating hospitals ( p<0.05 ; table 1 ) . furthermore , cms - nsqip participating hospitals more frequently were accredited by the commission on cancer , had an acgme residency training program , and were coth members compared to non - participating hospitals ( p<0.05 ) . however , on multivariable analysis , only coth membership remained a significant predictor of initial cms - nsqip public reporting participation ( or=2.45 , ci : 1.12 , 5.35 ; table 2 ) . after adjusting for multiple comparisons in bivariate analyses for each process , hcahps , and outcome measure , only the heart attack patient given aspirin at arrival  and  accidental puncture or laceration  measures were significantly different between participants and non - participants ( p<0.001 , appendix 1 , online only ) . the remaining 54 ( 96.6 % ) of these 58 process , hcahps , and outcomes measures showed no significant differences between cms - nsqip participating and non - participating hospitals . after adjusting for number of beds , coth membership , and hospital control / ownership , performance on 54 of the 58 quality measures was also not associated with participation in cms - nsqip public reporting ( appendix 1 , online only ) . there were four measures where poor performance was associated with participation : ( 1 )  accidental puncture or laceration  measure ( or=2.11 , ci : 1.04 , 4.30 ) ; ( 2 )  heart attack patient given aspirin at arrival  measure ( or= 0.26 , ci:0.10 , 0.64 ) ; ( 3 )  heart attack patient given aspirin at discharge ( or=0.38 , ci:0.16 , 0.87 ) ; and ( 4 )  definitely recommending the hospital to friends and family  ( or = 0.28 , ci : 0.11 , 0.71 ) . next , the performance of cms - nsqip participating vs. non - participating hospitals was compared to determine whether only the better performing hospitals chose to publicly report their acs nsqip outcomes . after excluding hospitals from analysis for any outcome that they reported data as  not available ,  71 hospitals reported the elderly surgery outcome , 62 reported colon surgery , and 31 hospitals reported lower extremity bypass outcomes ( table 3 ) . a greater proportion of cms - nsqip public reporting participants ( 18.3% ) were better - than - average  performers on the elderly surgery outcome than the percentage of  better - than - average performers  from the overall acs nsqip hospital population ( 9.2% , p<0.05 ; table 3 ) . however , no differences were observed between cms - nsqip participants and non - participants for the colon surgery or lower extremity bypass outcome measures . for the elderly surgery outcome , fewer cms - nsqip participants ( 2.8% ) reported  worse - than - average  outcomes compared to the acs nsqip hospital population as a whole ( 13.6% , p<0.01 ) . no differences were seen on  worse - than - average  performance for the colon surgery outcome or the lower extremity bypass outcome ( table 3 ) . in wave two of cms - nsqip public reporting , there were an additional 22 hospitals that elected to participate ( n=102 hospitals ) . similar to wave one initial participation , cms - nsqip participants in wave two had a higher proportion of hospitals that reported  better - than - average ( 18.2% ) than was found among all acs nsqip hospitals ( 9.2% , p<0.05 ) for the elderly surgery measure ( results not shown ) . accordingly , fewer cms - nsqip participants reported  worse - than - average  ( 5.7% ) outcomes than the proportion who reported  worse - than - average  in the acs nsqip hospital population as a whole ( 13.6% ; p<0.05 ) . no differences were found between cms - nsqip hospitals and the acs nsqip hospitals for the  colon surgery  or importantly , in comparing wave one and wave two for the elderly surgery group , a larger percentage of new wave two cms - nsqip participating hospitals reported  worse - than - average  performance ( 17.6% ) than was reported during initial wave one participation ( 2.8% ) . overall , acs nsqip hospitals ( n=452 ) had a mean of 237 ( standard deviation ( sd ) = 157 ) general medical and surgical adult beds , 21,145 ( sd=14,806 ) annual admissions , and 6,488 ( sd=5,140 ) inpatient surgical operations ( table 1 ) . the majority were jcaho accredited ( 92.4% ) , commission on cancer accredited ( 70.8% ) , and had acgme residency training programs ( 61.3% ) and/or coth accreditation ( 34.3% ) . in addition , 89.1% reported the  dissemination of reports to the community on quality and cost of service ,  while 95.9% reported  tracking and communicating clinical health information across their organization .  in comparing cms - nsqip public reporting participants and non - participants , cms - nsqip participating hospitals had larger number of hospital beds , admissions , medicare discharges , inpatient and outpatient surgical operations , and hospital operating rooms compared to non - participating hospitals ( p<0.05 ; table 1 ) . furthermore , cms - nsqip participating hospitals more frequently were accredited by the commission on cancer , had an acgme residency training program , and were coth members compared to non - participating hospitals ( p<0.05 ) . however , on multivariable analysis , only coth membership remained a significant predictor of initial cms - nsqip public reporting participation ( or=2.45 , ci : 1.12 , 5.35 ; table 2 ) . after adjusting for multiple comparisons in bivariate analyses for each process , hcahps , and outcome measure , only the heart attack patient given aspirin at arrival  and  accidental puncture or laceration  measures were significantly different between participants and non - participants ( p<0.001 , appendix 1 , online only ) . the remaining 54 ( 96.6 % ) of these 58 process , hcahps , and outcomes measures showed no significant differences between cms - nsqip participating and non - participating hospitals . after adjusting for number of beds , coth membership , and hospital control / ownership , performance on 54 of the 58 quality measures was also not associated with participation in cms - nsqip public reporting ( appendix 1 , online only ) . there were four measures where poor performance was associated with participation : ( 1 )  accidental puncture or laceration  measure ( or=2.11 , ci : 1.04 , 4.30 ) ; ( 2 )  heart attack patient given aspirin at arrival  measure ( or= 0.26 , ci:0.10 , 0.64 ) ; ( 3 )  heart attack patient given aspirin at discharge  ( or=0.38 , ci:0.16 , 0.87 ) ; and ( 4 )  definitely recommending the hospital to friends and family  ( or = 0.28 , ci : 0.11 , 0.71 ) . next , the performance of cms - nsqip participating vs. non - participating hospitals was compared to determine whether only the better performing hospitals chose to publicly report their acs nsqip outcomes . after excluding hospitals from analysis for any outcome that they reported data as  not available ,  71 hospitals reported the elderly surgery outcome , 62 reported colon surgery , and 31 hospitals reported lower extremity bypass outcomes ( table 3 ) . a greater proportion of cms - nsqip public reporting participants ( 18.3% ) were  better - than - average  performers on the elderly surgery outcome than the percentage of  better - than - average performers  from the overall acs nsqip hospital population ( 9.2% , p<0.05 ; table 3 ) . however , no differences were observed between cms - nsqip participants and non - participants for the colon surgery or lower extremity bypass outcome measures . for the elderly surgery outcome , fewer cms - nsqip participants ( 2.8% ) reported  worse - than - average  outcomes compared to the acs nsqip hospital population as a whole ( 13.6% , p<0.01 ) . no differences were seen on  worse - than - average  performance for the colon surgery outcome or the lower extremity bypass outcome ( table 3 ) . in wave two of cms - nsqip public reporting , there were an additional 22 hospitals that elected to participate ( n=102 hospitals ) . similar to wave one initial participation , cms - nsqip participants in wave two had a higher proportion of hospitals that reported  better - than - average  ( 18.2% ) than was found among all acs nsqip hospitals ( 9.2% , p<0.05 ) for the elderly surgery measure ( results not shown ) . accordingly , fewer cms - nsqip participants reported  worse - than - average  ( 5.7% ) outcomes than the proportion who reported  worse - than - average  in the acs nsqip hospital population as a whole ( 13.6% ; p<0.05 ) . no differences were found between cms - nsqip hospitals and the acs nsqip hospitals for the  colon surgery  or  lower extremity bypass  outcomes . importantly , in comparing wave one and wave two for the elderly surgery group , a larger percentage of new wave two cms - nsqip participating hospitals reported  worse - than - average  performance ( 17.6% ) than was reported during initial wave one participation ( 2.8% ) . public reporting and transparency are being demanded by multiple stakeholders . until recently , there were very little data reported publicly regarding surgical outcomes . with the recent option for acs nsqip hospitals to voluntarily report their outcomes on hospital compare , we were able to study the characteristics of the hospitals that initially opted to participate . we found that only 17.5% of hospitals chose to publicly report , but there were very few differences in hospital characteristics and other publicly reported measures between hospitals that chose to participate and those that did not . this suggests that some unmeasured factor likely drives the decision to publicly report outcomes , such as the institution s culture and interest in transparency . although hospitals are increasingly releasing information about the quality of care that they provide , there has been a general reluctance to release too much information for a variety of reasons . these concerns include questioning the validity and accuracy of the data reported , inadequate risk adjustment , and the fear of unintended consequences , such as  cherry picking ( hospitals selecting lower - risk patients to avoid poorer outcomes ) or losing patients to better performing hospitals . moreover , our work has suggested that surgeons are also reluctant to publicly report their outcomes , or the hospitals outcomes , because of fear that the patient will misinterpret the data , fear of personal / professional vulnerability , and of  dishonest gaming  of the public reporting system . hospitals have long been compared on outcomes using data collected for billing , and these data have been shown to be inaccurate . these inaccuracies may have created mistrust , and this may be partly responsible for the low initial participation rate that we observed . however , acs nsqip data are clinically collected and thought to be far more accurate than administrative data with respect to postoperative outcomes , so hospital concern regarding the validity of these data should be less . this study is the first , to our knowledge , to examine hospital characteristics and quality of care differences between hospitals that voluntarily chose to report their surgical outcomes on hospital compare , compared to a group that did not . little is known about what drives some hospitals to participate in public reporting ; particularly when there are no financial incentives involved , as with the cms - nsqip initiative . we found that of all possible hospital structural characteristics , only teaching hospital status predicted participation in the cms - nsqip public reporting initiative . it is unclear why teaching hospitals would have increased participation , but a culture of research , innovation and first - mover leadership may lead to an earlier interest in transparency and public reporting . this first mover leadership and increased interest in quality improvement and transparency among teaching hospitals is evidenced by the recent uptake of the nsqip quality in - training initiative ( qiti ) which aims to integrate outcomes data into surgical education during general surgery residency . although public reporting has been a key factor in stimulating hospital quality - improvement initiatives and improving process metrics , debate remains on the true measureable effect of public reporting on outcome measures . we hypothesized that the hospitals with better publicly reported performance on existing hospital compare measures would be more likely to participate in the cms - nsqip initiative . our unadjusted results show that some differences exist between participating and non - participating hospitals on process and outcome measures . however , after controlling for confounders , the majority of the associations disappeared ; leaving only a few inconsistent differences between participants and non - participants . this suggests that the decision to publicly report is likely not based solely on a hospital s knowledge of their current or prior performance , but rather related to the hospital s culture and attitudes surrounding transparency . finally , we examined if a larger proportion of  better - performing  hospitals were cms - nsqip participants than acs nsqip hospitals as a whole . better than average  performance for the elderly surgery outcome than the asc nsqip population overall . this higher percentage of better performing hospitals reporting may be due to the fact that hospitals were able to see their outcomes before deciding to participate . however , we did not see this same trend among the  colon surgery  outcome . second , analyses of the second wave of cms - nsqip participants showed an interesting trend . in the second wave of cms - nsqip public reporting , a larger proportion of hospitals with a designation for elderly surgery and colon surgery outcomes chose to participate compared to the first wave . even though these hospitals were aware that their outcomes would be reported as  worse - than - average ,  they still elected to publicly report these data . the sample of hospitals used , acs nsqip hospitals , may not be representative of all hospitals in the united states . hospitals that participate in acs nsqip do so voluntarily and pay a fee for their participation making them a self - selected group with an interest in quality improvement and possibly public reporting . this may also lead to less variation in the measures examined than if all u.s . second , the small number of hospitals reporting better - than - average and worse - than - average for acs - nsqip surgical outcomes makes comparisons difficult . better  or  worse  than average is a function of the acs nsqip modeling technique itself ; which shrinks the majority of hospitals toward the mean and classifies them as average . nonetheless , it is interesting to note which hospitals participate in public reporting , particularly when a  worse - than - expected  hospital voluntarily participates and publicly reports their poor outcomes . finally , our comparisons are limited to the available hospital characteristics and outcome measures currently collected . there may be other unknown factors that better explain why hospitals choose to participate in public reporting ( e.g. , engagement of the board of directors in quality measurement ) . our study explored possible reasons for initial participation in the public reporting of surgical outcomes on hospital compare . we found few differences between cms - nsqip public reporting participants and non - participants in terms of hospital characteristics or performance on other publicly reported quality measures . the reasons why hospitals elect to participate is still unclear , but their past and current performance generally does not drive participation . thus , a hospital culture that focuses on quality measurement and promotes transparency may explain the results .
backgroundin october 2012 , the centers for medicare and medicaid services ( cms ) began publicly reporting american college of surgeons national surgical quality improvement program ( acs nsqip ) surgical outcomes on its public reporting website , hospital compare . 
 participation in this cms - nsqip initiative is voluntary . our objective was to compare 
 cms - nsqip participating hospitals to acs nsqip hospitals that elected not to participate.study designhospital compare and american hospital association annual survey data were merged to compare cms - nsqip participants to non - participants . 
 regression models were developed to assess predictors of participation and to assess if hospitals differed on 32 process , 10 patient experience ( hcahps ) , and 16 outcome ( hospital compare & ahrq ) measures . 
 additionally , performance on two waves of publicly reported acs nsqip surgical outcome measures was compared.resultsof the 452 acs nsqip hospitals , 80 ( 18% ) participated in cms - nsqip public reporting . 
 participating hospitals had more beds , admissions , operations , and were more often accredited ( commission on cancer and the council of teaching hospitals ( coth ) ( p<0.05 ) . 
 only coth membership remained significant in adjusted analyses ( or 2.45 , 95% ci 1.125.35 ) . 
 hospital performance on process , hcahps , and outcome measures were not associated with cms - nsqip participation for 54 of 58 measures examined . 
 hospitals with 
 better - than - average  performance were more likely to publicly report the elderly surgery measure ( p<0.05 ) . 
 in wave two , an increased proportion of new participants reported  worse - than - average  outcomes.conclusionsthere were few measurable differences between cms - nsqip participating and non - participating hospitals . the decision to voluntarily publicly report 
 may be related to the hospital s culture of quality improvement and transparency .