***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 The purpose of this study was to use MRI to classify acute grade one hamstring muscle strains in Australian Rules footballers to determine if it was accurate in predicting the recovery time for each injury and also able to predict those that would recur within the same season . A prospect i ve study was performed over five years at a professional Australian Football League club . Thirty-one acute grade one hamstring injuries underwent MRI examination  within 24 - 72 hours following the injury . Each injury underwent the same rehabilitation programme . The rehabilitation interval ( RI ) was the time in days for the player to resume full team training . Fourteen ( 45 % ) of the injuries were normal on MRI . Seventeen ( 55 % ) were abnormal with a hyperintense T2 lesion on the axial fat suppressed views . The MRI negative group had a significantly faster RI ( 6.6 days ) compared with the MRI positive group ( 20.2 days ) . Both the length and cross sectional area ( CSA ) of the MRI positive lesions were measured . The length of the lesion had a stronger correlation coefficient with the RI ( 0.84 ) than did the CSA ( 0.76 ) . Six of the 17 MRI positive strains recurred with no correlation found between the lesion 's length or CSA , or the RI . None of the 14 MRI negative injuries recurred . The study confirms that MRI can aid in the investigation of acute grade one hamstring muscle strains in predicting recovery time . However the size of the initial strain or the RI do not seem to be reliable indicators in predicting those strains that might recur STUDY DESIGN Prospect i ve cohort study . OBJECTIVE To examine clinical and magnetic resonance imaging ( MRI ) features of hamstring muscle injury to determine if any are predictive for recurrent injury . BACKGROUND Hamstring muscle strain injury and subsequent recurrent injury are common . Little information exists on factors that may increase the risk for recurrent injury . METHODS AND MEASURES The subjects were athletes from 3 professional Australian Rules football teams ( n = 162 ) .  Anthropometric measurements , clinical signs , convalescent interval , and MRI assessment and measurement were undertaken and recorded in athletes with hamstring muscle strain injury . Athletes were followed for the presence , or absence , of recurrent injury to the same-side posterior thigh over the same and subsequent playing seasons . RESULTS Thirty athletes met criteria for hamstring injury . Twelve ( 40 % ) of 30 athletes had recurrent injury within the same season , with an additional 7 athletes having recurrent injury in the subsequent season . None of the features examined were associated with increased recurrent injury risk within the same playing season . Statistical analysis demonstrated that when combining the same with the subsequent playing season a larger size of initial hamstring injury , as measured by MRI , was associated with an increased risk for recurrent injury ( P<.01 ) . A measured transverse size of injury greater than 55 % of the muscle , or calculated volume of injury greater than 21.8 cm3 , result ed in an increased risk for hamstring recurrence of 2.2 ( 95 % CI , 0.88 - 5.32 ) and 2.3 ( 95 % CI , 0.94 - 5.81 ) times , respectively , when compared to athletes with hamstring injuries below these measurements . CONCLUSIONS A larger size of hamstring injury was indicative of higher risk for recurrent injury but only after the subsequent playing season was considered along with the same playing season . None of the other parameters tested , including a shorter convalescent interval and clinical features , were associated with an increased risk for recurrent injury . However , due to low sample size the certainty of these conclusions may be limited Background Hamstring injury is the single most common injury in professional football .  MRI is commonly used to confirm the diagnosis and provide a prognosis of lay-off time . Objective To evaluate the use of  MRI  as a prognostic tool for lay-off after hamstring injuries in professional football players and to study the association between MRI findings and injury circumstances . Methods Prospect i ve cohort study where 23 European professional teams , were followed between 2007 and 2011 . Team medical staffs recorded individual player exposure and time-loss injuries . Radiological grading was performed using a modified Peetrons classification into four grade s where grade s 2 and 3 represent fibre disruption . Results In total , 516 hamstring injuries occurred and 58 % of these were examined by MRI .  Thirteen per cent were grade 0 injuries , 57 % grade 1 , 27 % of grade 2 and 3 % of grade 3 . Grade 0 and 1 injuries accounted for 56 % ( 2141/3830 days ) of the total lay-off . The lay-off time differed between all four radiological grade s of injury ( 8±3 , 17±10 , 22±11 and 73±60 days , p<0.0001 ) . Eighty-three per cent of injuries affected the biceps femoris while 11 % and 5 % occurred to the semimembranosus and semitendinosus , respectively . Re-injuries ( N=34/207 ) constituted 16 % of injuries . All re-injuries occurred to the biceps femoris . Conclusion MRI can be helpful in verifying the diagnosis of a hamstring injury and to prognosticate lay-off time . Radiological grading is associated with lay-off times after injury . Seventy per cent 
    Output:
    
No strong evidence for any  MRI finding as a risk factor for hamstring re-injury was found .
There was moderate evidence that intratendinous injuries were associated with increased re-injury risk .
Post hoc analysis showed moderate evidence that injury to the biceps femoris was a moderate to strong risk factor for re-injury .
Conclusion There is currently no strong evidence for any MRI finding in predicting hamstring re-injury risk .
Intratendinous injuries and biceps femoris injuries showed moderate evidence for association with a higher re-injury risk .