***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: BACKGROUND Results from observational studies suggest that micronutrient status is a determinant of the progression of human immunodeficiency virus ( HIV ) disease . METHODS We enrolled 1078 pregnant women infected with HIV in a double-blind , placebo-controlled trial in Dar es Salaam , Tanzania , to examine the effects of daily supplements of vitamin A ( preformed vitamin A and beta carotene ) , multivitamins ( vitamins B , C , and E ) , or both on progression of HIV disease , using survival  models . The median follow-up with respect to survival was 71 months ( interquartile range , 46 to 80 ) . RESULTS Of 271 women who received multivitamins  , 67 had progression to World Health Organization ( WHO ) stage 4 disease or died -- the primary outcome --as compared with 83 of 267 women who received placebo ( 24.7 percent vs. 31.1 percent ; relative risk , 0.71 ; 95 percent confidence interval , 0.51 to 0.98 ; P=0.04 ) . This regimen was also associated with reductions in the relative risk of death related to the acquired immunodeficiency syndrome ( 0.73 ; 95 percent confidence interval , 0.51 to 1.04 ; P=0.09 ) , progression to WHO stage 4 ( 0.50 ; 95 percent confidence interval , 0.28 to 0.90 ; P=0.02 ) , or progression to stage 3 or higher ( 0.72 ; 95 percent confidence interval , 0.58 to 0.90 ; P=0.003 ) . Multivitamins also result ed in significantly higher CD4 + and CD8 + cell counts and significantly lower viral loads . The effects of receiving vitamin A alone were smaller and for the most part not significantly different from those produced by placebo . Adding vitamin A to the multivitamin regimen reduced the benefit with regard to some of the end points examined . CONCLUSIONS Multivitamin supplements delay the progression of HIV disease and provide an effective , low-cost means of delaying the initiation of antiretroviral therapy in HIV-infected women BACKGROUND Multiple micronutrient deficiencies may contribute to low birth weight , which is a major global determinant of mortality . OBJECTIVE We assessed the effect of prenatal multimicronutrient supplementation on gestational length and birth size . DESIGN We conducted a r and omized , placebo-controlled , double-blind effectiveness trial among antenatal care attendees in Harare , Zimbabwe . Pregnant women ( 22 - 35 wk of gestation ) were r and omly allocated to receive a multimicronutrient or placebo supplement daily until delivery . Supplementation with iron and folic acid was part of antenatal care . RESULTS Of 1669 women , birth data were available from 1106 ( 66 % ) , of whom 360 ( 33 % ) had HIV infection . The mean gestational length was 39.1 wk , and 16.6 % of the women had a gestational length < 37 wk . The mean birth weight was 3030 g , and 10.5 % of the infants had a birth weight < 2500 g. Multimicronutrient supplementation was associated with tendencies for increased gestational length ( 0.3 wk ; 95 % CI : -0.04 , 0.6 wk ; P = 0.06 ) , birth weight ( 49 g ; -6 , 104 g ; P = 0.08 ) , and head circumference ( 0.2 cm ; -0.02 , 0.4 cm ; P = 0.07 ) but was not associated with low birth weight ( birth weight < 2500 g ) ( relative risk : 0.84 ; 0.59 , 1.18 ; P = 0.31 ) . The effect of multimicronutrient supplementation on birth weight was not significantly different between HIV-uninfected ( 26 g ; -38 , 91 g ) and HIV-infected ( 101 g ; -3 , 205 g ) subjects ( interaction , P > 0.10 ) . CONCLUSION Antenatal multimicronutrient supplementation may be one strategy to increase birth size Selenium deficiency has been implicated in accelerated disease progression and poorer survival among population s infected with HIV in developed countries , yet these associations remain unexamined in developing countries . Among 949 HIV-1-infected Tanzanian women who were pregnant , we prospect ively examined the association between plasma selenium levels and survival and CD4 counts over time . Over the 5.7-y median follow-up time , 306 of 949 women died . In a Cox multivariate model , lower plasma selenium levels were significantly associated with an increased risk of mortality ( P-value , test for trend = 0.01 ) . Each 0.1 micromol/L increase in plasma selenium levels was related to a 5 % ( 95 % CI = 0%-9 % ) decreased risk of mortality . Plasma selenium levels were not associated with time to progression to CD4 cell count < 200 cells/mm(3 ) but were weakly and positively related to CD4 cell count in the first years of follow up . Selenium status may be important for clinical outcomes related to HIV disease in sub-Saharan Africa Systematic Review Series Series Editors : Cynthia Mulrow , MD , MSc Deborah Cook , MD , MSc The last article in this series outlined methods with which to search the literature for studies on the clinical question that generates a systematic review [ 1 ] . Herein , we discuss the subsequent steps of selecting and appraising  studies  for a review . Both of these steps involve important judgments that can influence the results of a review . In selecting studies , review ers judge the relevance of the studies to the review question . In appraising studies , review ers judge numerous features of design and analysis . Some of these judgments are easy to make ; others are more difficult and prone to error . To be confident in their decisions , review ers should use methods that are reliable ( the results do not change if the procedure is repeated ) , impartial ( not influenced by the study results ) , and explicit ( unambiguous ) [ 2 ] . These strategies for selection and appraisal are sensible , and they distinguish most systematic review s from most narrative review s. However , evidence to support the importance of some of the methods we suggest is either scant or conflicting ; readers are referred to the original research on these approaches for more details . Selecting Studies for Systematic Review s If review ers perform a comprehensive search of the literature using the methods described previously in this series [ 1 ] , they will probably have assembled a large sample of articles . This sample will include most ( ideally , all ) studies that are relevant to the review question ( that is , the sensitivity of the search will be high ) . Inevitably , because such a wide net is cast , articles not pertinent to the clinical question will be retrieved ( that is , the specificity of the search will be modest ) . Thus , the review ers ' next task is to sort through all of the potentially relevant articles and select those that will be included in the review . To do so , review ers adopt several of the tactics listed in Table 1 and Table 2 for planning and executing the selection process ( in effect , improving the specificity of the search ) ; these tactics are described below . Table 1 . Planning Study Selection Table 2 . Strategies for Selecting and Appraising Studies Begin with a Well-Built Clinical Question Review ers should ensure that the question for review includes the four elements of a well-built clinical question [ 3 , 4 ] : the patients of interest , the main interventions under investigation , the comparison interventions , and the clinical outcomes of interest . By including these four elements , review ers can better focus the selection process . Choose Selection Criteria That Fit the Clinical Question Consider a systematic review of the effectiveness of a drug treatment ( for example , a proton-pump inhibitor ) for patients with a particular disorder ( such as esophageal reflux ) . Review ers need to decide whether to include studies of patients with any symptoms of reflux , only those with classic symptoms , or only those in whom definitive diagnostic tests have confirmed the presence of reflux . In addition , review ers might choose to include studies of patients with different comorbid conditions ; patients from different demographic or geographic or cultural background s ; or patients from different health systems , such as inpatient or community population s. Similarly , review ers should use selection criteria that reflect the main and comparison interventions of interest . In our esophageal reflux example , review ers would need to decide whether to include studies of a particular drug or studies of all agents in that drug 's class and whether to include studies of any dose and regimen or only studies with a specific regimen . For the comparison interventions , the review ers would decide whether to include studies that compare the experimental drug with alternate treatments ( such as antacids or histamine-2-receptor antagonists ) , with placebo , or with both . For the clinical outcomes , review ers have analogous tasks of defining the outcomes and translating them into criteria . In our example , the review ers would start by listing each clinical outcome ( for example , whether the outcome was endoscopic or clinical and whether it focused on cure or persistence ) and then decide whether to include studies that reported any outcome or only those with certain clinical ly important outcomes ( such as improvement in symptoms at 1 year ) . After thoroughly considering each element of the review question , review ers compile a set of explicit selection criteria . When these criteria are not explicit , the results of the review are more prone to error [ 5 , 6 ] . Reporting the selection criteria used in a review is extremely important to readers because the criteria indicate the relevance of the review to the readers ' clinical practice . Specify the Types of Study Design To Be Included After creating selection criteria that appropriately reflect the review question , review ers should consider which study design s to include . Ideally , review ers choose study design s that are most likely to produce valid results . For example , to answer questions about therapy or harm , review ers may want to include r and omized trials [ 7 ] because they provide more accurate estimates of benefit or harm than do cohort studies , casecontrol studies , and case series [ 8 ] . In reality , however , r and omized trials may not be conducted to address questions of harm [ 9 ] . Therefore , review ers need to consider which study design s are likely to be available to answer their question ; this information may necessitate modification of originally conceptualized selection criteria to incorporate observational ( nonexperimental ) studies . Specify Criteria Related to Type and Form of Publication Review ers also need to consider issues related to type and form of publication . Ideally , all of the relevant studies would be published as peer- review ed journal articles . However , some completed studies may be published only as abstract s , in non-peer- review ed form , or not at all . Review ers decide whether to include these incompletely reported studies when planning their literature search . By including all articles in various stages of publication and subjecting them to rigorous critical appraisal , review ers minimize the threat of publication bias ( the preferential reporting of studies with positive results ) [ 10 - 12 ] , which could generate misleading review s. Other studies may be reported more than once . To avoid over-representing duplicate studies in the review , investigators should plan to look for and exclude duplicate publications [ 13 ] . Finally , because studies may be published in different language s and because excluding studies published in different language s may bias the results of review s [ 14 , 15 ] , articles should be included , as appropriate , regardless of the language of publication ( translating as necessary ) . Limited time and re sources , however , may preclude such an approach . Construct and Pretest Selection Forms After deciding on selection criteria , review ers can prepare customized forms that contain checklists of the selection criteria ( Figure 1 ) . Using these forms can simplify the selection process , increase reliability , and provide a record of the judgments made about each study . After drafting form prototypes , review ers pretest these forms for clarity , ease of application , and reliability . To pretest the forms , two or more independent review ers typically apply them to a r and om sample of studies identified by the literature search . Review ers compare their results to identify sources of ambiguity and then revise the forms accordingly . If the revisions are substantial , this process may need to be repeated before the forms can be used . Figure 1 . Example of a form that might be developed for the selection of studies for a systematic review evaluating the efficacy of -blockers for secondary prevention of variceal bleeding .  Write a Detailed Protocol Having a selection protocol as part of a larger protocol for the entire review helps review ers in two ways . First , it provides a document that explicitly states the review question and the selection criteria , making the process accountable . Review ers can later return to the protocol for guidance in resolving disagreements about article selection . Second , the selection protocol identifies what work will be done , by whom , in what manner , when , and for what reason ; thus , it provides a mode of communication within the review team . When review ers have a very large sample of studies from which to select , they can simplify this task by review ing all of the titles , then the abstract s , and then the full articles , excluding studies that do not meet one or more selection criteria at each step . In doing so , review ers should record ( on the selection forms ) the reasons for exclusion . After review ers have selected studies for the systematic review , they will move to the next task of critical appraisal . This procedure also requires careful planning . Appraising Studies for Systematic Review s Review ers appraise the studies selected for review with three objectives in mind : 1 ) to underst and the validity of the studies , 2 ) to uncover reasons for differences among study results other than chance , and 3 ) to provide readers with sufficient information with which to judge for themselves the applicability of the systematic review to their clinical practice . To achieve these goals , review ers use the strategies outlined in Table 2 and Table 3 to carefully reexamine many important features of the primary studies . Table 3 . Planning Study Appraisal Examine Important Clinical Features Although the selection criteria for a systematic review define the population , interventions , and outcomes of interest , the appraisal process involves a detailed assessment of the patients ( for example , high , medium , or low risk ) , the study interventions ( for example , frequency , degree , and duration ) , and the outcome measurements ( for example , 
    Output:
    
Conclusion R and omized trials of vitamins to prevent MTCT have yielded conflicting results without strong evidence of benefit and have failed to exclude the possibility of harm