***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Prognosis studies are investigations of future events or the evaluation of associations between risk factors and health outcomes in population s of patients ( 1 ) . The results of such studies improve our underst and ing of the clinical course of a disease and assist clinicians in making informed decisions about how best to manage patients . Prognostic research also informs the design of intervention studies by helping define subgroups of patients who may benefit from a new treatment and by providing necessary information about the natural history of a disorder ( 2 ) . There has recently been a rapid increase in the use of systematic review methods to synthesize the evidence on research questions related to prognosis . It is essential that investigators conducting systematic review s thoroughly appraise the method ologic quality of included studies to be confident that a study 's design , conduct , analysis , and interpretation have adequately reduced the opportunity for bias ( 3 , 4 ) . Caution is warranted , however , because inclusion of method ologically weak studies can threaten the internal validity of a systematic review ( 4 ) . This follows abundant empirical evidence that inadequate attention to biases can cause invalid results and inferences ( 5 - 9 ) . However , there is limited consensus on how to appraise the quality of prognosis studies ( 1 ) . A useful framework to assess bias in such studies follows the basic principles of epidemiologic research ( 10 , 11 ) . We focus on 6 areas of potential bias : study participation , study attrition , prognostic factor measurement , confounding measurement and account , outcome measurement , and analysis . The main objectives of our review of review s are to describe methods used to assess the quality of prognosis studies and to describe how well current practice s assess potential biases . Our secondary objective is to develop recommendations to guide future quality appraisal , both within single studies of prognostic factors and within systematic review s of the evidence . We hope this work facilitates future discussion and research on biases in prognosis studies and systematic review s. Methods Literature Search and Study Selection We identified systematic review s of prognosis studies by search ing MEDLINE ( 1966 to October 2005 ) using the search strategy recommended by McKibbon and colleagues ( 12 ) . This strategy combines broad search terms for systematic review s ( systematic review .mp ; meta- analysis .mp ) and a sensitive search strategy for prognosis studies ( cohort , incidence , mortality , follow-up studies , prognos * , predict * , or course ) . We also search ed the reference lists of included review s and method ologic papers to identify other relevant publications . We restricted our search to English- language publications . One review er conducted the search and selected the studies . Systematic review s , defined as review s of published studies with a comprehensive search and systematic selection , were included if they assessed the method ologic quality of the included studies by using 1 or more explicit criteria . We excluded studies if they were meta-analyses of independent patient data only , if their primary goal was to investigate the effectiveness of an intervention or specific diagnostic or screening tests , or if they included studies that were not done on humans . Data Extraction and Synthesis Individual items included in the quality assessment of the systematic review s were recorded as they were reported in the publication ( that is , the information that would be available to readers and future review ers ) . We review ed journal Web sites and contacted the authors of the systematic review s for additional information when authors made such an offer in their original papers . When review s assessed different study design s by using different sets of quality items , we extracted only those items used to assess cohort studies . We constructed a comprehensive list of distinct items that the review s used to assess the quality of their included studies . The full text of each review was screened . All items used by the review authors to assess the quality of studies were extracted into a computerized spreadsheet by 1 review er . Two experienced review ers , a clinical epidemiologist and an epidemiologist , independently synthesized the quality items extracted from the prognosis review s to determine how well the systematic review s assessed potential biases . We did this in 3 steps : 1 ) identified distinct concepts or domains addressed by the quality items ; 2 ) grouped each extracted quality item into the appropriate domain or domains ; and 3 ) identified the domains necessary to assess potential biases in prognosis studies . We then used this information to assess how well the review s ' quality assessment included items from the domains necessary to assess potential biases . After completing each of the first 3 steps , the review ers met to attempt to reach a consensus . The consensus process involved each review er presenting his or her observations and results , followed by discussion and debate . A third review er was available in cases of persistent disagreement or uncertainty . In the first step , all domains addressed by the quality items were identified . The first review er iteratively and progressively defined the domains as items were extracted from the included review s. The second review er defined domains from a r and om list of all extracted quality items . Limited guidance was provided to the review ers so that their assessment s and definitions of domains would be independent . The review ers agreed on a final set of domains that adequately and completely defined all of the extracted items . In the second step , review ers independently grouped each extracted item into the appropriate domains . Review ers considered each extracted item by asking , What is each particular quality item addressing ? or What are the review 's authors getting at with the particular quality assessment item ? . Items were grouped into the domain or domains that best represented the concepts being addressed . For example , the extracted items at least 80 % of the group originally identified was located for follow-up and follow-up was sufficiently complete or does n't jeopardize validity were each independently classified by both review ers as assessing the domain completeness of follow-up adequate , whereas the extracted item quantification and description of all subjects lost to follow-up was classified as assessing the domain completeness of follow-up described . In the third step , we identified the domains necessary to assess potential biases . Each review er considered the ability of the identified domains to adequately address , at least in part , 1 of the following 6 potential biases : 1 ) study participation , 2 ) study attrition , 3 ) prognostic factor measurement , 4 ) confounding measurement and account , 5 ) outcome measurement , and 6 ) analysis . Domains were considered to adequately address part of the framework if information garnered from that domain would inform the assessment of potential bias . For example , both review ers judged that the identified domain study population represents source population or population of interest assessed potential bias in a prognosis study , whereas the domain research question definition did not , although the latter is an important consideration in assessing the inclusion of studies in a systematic review . Finally , on the basis of our previous ratings , we looked at whether each review included items from the domains necessary to assess the 6 potential biases . We calculated the frequency of systematic review s by assessing each potential bias and the number of review s that adequately assessed bias overall . From this systematic synthesis , we developed recommendations for improving quality appraisal in future systematic review s of prognosis studies . We used Microsoft Access and Excel 2002 ( Microsoft Corp. , Redmond , Washington ) for data management and SAS for Windows , version 9.1 ( SAS Institute , Inc. , Cary , North Carolina ) for descriptive statistics . Role of the Funding Sources The funding sources , the Canadian Institutes of Health Research , the Canadian Chiropractic Research Foundation , the Ontario Chiropractic Association , and the Ontario Ministry of Health and Long Term Care , did not have a role in the collection , analysis , or interpretation of the data or in the decision to su bmi t the manuscript for publication . Results We identified 1384 potentially relevant articles . Figure 1 shows a flow chart of studies that were included and excluded . Figure 2 shows the number of review s identified by year of publication . We excluded 131 systematic review s of prognosis studies that did not seem to include any quality assessment of the included studies ; this represented 44 % of prognosis review s. We included 163 review s of prognosis studies in our analysis ( 13 - 175 ) . The most common topics were cancer ( 15 % ) , musculoskeletal disorders and rheumatology ( 13 % ) , cardiovascular ( 10 % ) , neurology ( 10 % ) , and obstetrics ( 10 % ) . Other review s included a wide range of health and health care topics . Sixty-three percent of the review s investigated the association between a specific prognostic factor and a particular outcome ; the remainder investigated multiple prognostic factors or models . The number of primary studies included in each systematic review ranged from 3 to 167 ( median , 18 [ interquartile range , 12 to 31 ] ) . A complete description of the included review s is available from the authors on request . Figure 1 . Flow diagram of inclusion and exclusion criteria of systematic review s. Figure 2 . Number of systematic review s of prognosis studies identified over time . Quality Items One hundred fifty-three review s provided adequate detail to allow extraction of quality items . Eight hundred eighty-two distinct quality items were extracted from the review s. Most review s developed their own set of quality items , with only a few applying criteria from previous review s. Most quality items Purpose : To compare percutaneous coronary intervention ( PCI ) using stent implantation versus coronary artery bypass graft ( CABG ) in patients with multiple vessel disease with involvement of the proximal left anterior descending coronary artery ( LAD ) . Methods : 230 patients with multiple vessel disease and severe stenosis of the proximal LAD ( 113 with PCI , 117 with CABG ) . They were a cohort of patients from the r and omised ERACI ( Argentine r and omized trial of percutaneous transluminal coronary angioplasty versus coronary artery bypass surgery in multivessel disease ) II study . Results : Both groups had similar baseline characteristics . There were no significant differences in 30 day major adverse cardiac events ( death , myocardial infa rct ion , stroke , and repeat procedures ) between the strategies ( PCI 2.7 % v CABG 7.6 % , p = 0.18 ) . There were no significant differences in survival ( PCI 96.4 % v CABG 95 % , p = 0.98 ) and survival with freedom from myocardial infa rct ion ( PCI 92 % v CABG 89 % , p = 0.94 ) at 41.5 ( 6 ) months ’ follow up . However , freedom from new revascularisation procedures ( CABG 96.6 % v PCI 73 % , p = 0.0002 ) and frequency of angina ( CABG 9.4 % v PCI 22 % , p = 0.025 ) were superior in the CABG group . Conclusion : Patients with multivessel disease and significant disease of the proximal LAD r and omly assigned in the ERACI II trial to PCI or CABG had similar survival and survival with freedom from myocardial infa rct ion at long term follow up . Repeat revascularisation procedures were higher in the PCI group Background —R and omized trials comparing coronary artery bypass graft surgery ( CABG ) with percutaneous coronary interventions ( PCIs ) for patients with multivessel coronary disease ( MVD ) report similar long-term survival for CABG and PCI . These studies used a highly selected population of patients and providers , and their results may not be generalizable to actual care . Our goal in this study was to compare long-term survival of MVD patients treated with CABG vs PCI in contemporary practice . Methods and Results —From our northern New Engl and registries of consecutive coronary revascularizations , we identified 10 198 CABG and 4295 PCI patients with MVD who may have been eligible for either procedure between 1994 and 2001 . Vital status was obtained by linkage to the National Death Index . Proportional-hazards regression was used to calculate hazard ratios ( HRs ) for survival in CABG vs PCI patients after adjustment for comorbidities and disease characteristics . CABG  patients were older ; had more comorbidities , more 3-vessel disease , and lower ejection fractions ; and were more completely revascularized . Adjusted long-term survival for patients with 3-vessel disease was better after CABG than PCI ( HR , 0.60 ; P<0.01 ) but not for patients with 2-vessel disease ( HR , 0.98 ; P=0.77 ) . The survival advantage of CABG for 3-vessel disease patients was present in all patient population s , including women , diabetics , and the elderly and in the era of high stent utilization . Conclusions —In contemporary practice , survival for patients with 3-vessel coronary disease is better after CABG than PCI , an observation that patients and physicians should carefully consider when deciding on a revascularization strategy Background —The optimal method of coronary revascularization in dialysis patients is controversial . The purpose of this study was to compare the long-term survival of dialysis patients in the United States after PTCA , coronary stenting , or CABG .  Methods and Results —Dialysis patients hospitalized from 1995 to 1998 for first coronary revascularization procedures after renal replacement therapy initiation were identified from the US Renal Data System data base .  All-cause and cardiac survival was estimated by the life-table method and compared by the log-rank test . The impact of independent predictors on survival was examined in a Cox regression model . The in-hospital mortality was 8.6 % for 6668 CABG patients , 6.4 % for 4836 PTCA patients , and 4.1 % for 4280 stent patients .  The 2-year all-cause survival ( mean±SEM ) was 56.4±1.4 % for CABG patients , 48.2±1.5 % for PTCA patients , and 48.4±2.0 % for stent patients ( P < 0.0001 ) . After comorbidity adjustment , the relative risk ( RR ) for CABG ( versus PTCA ) patients was 0.80 ( 95 % CI 0.76 to 0.84 , P < 0.0001 ) for all-cause death and 0.72 ( 95 % CI 0.67 to 0.77 , P < 0.0001 ) for cardiac death . For stent ( versus PTCA ) patients , the RR was 
    Output:
    
In an exploratory meta- analysis , short-term mortality was higher after CABG compared to PCI .
A substantial number of patients died over a subsequent 1 to 5 yr , with no difference in mortality after CABG compared to PCI .