Bland-Altman Agreement Analysis in Laboratory Research

flavorless-Altman Agreement Analysis in science lab enquiryUse of Bland-Altman organisation compendium in science lab query A survey of live inform standards.Introduction-Advances in technology have take to development of new instruments and measurement devices in field of medicine. The clinicians and re take careers often strike to compare a newer mode of measurement with an established mavin, to check for interchangeability. man assessing for interchangeability the emphasis should be on testing how well 2 rules agree with each opposite. Earlier Pearsons product-moment correlation coefficient was utilise as a measure of parallelismR. However the approach was in entrance as this coefficient moreover indicated association rather than correspondence R. Hence Bland and Altman in their series of publicationsR stressed on quantification of bias. They provided a simpler and visually attractive patch for agreement abbreviation of endless variables measured on the same scale.RAfter its innovation to medical literature in 1983, the Bland-Altmans (B-A) method R is one of nearly comm solitary(prenominal) used statistical method for agreement analysis. The method is extensively used in evaluating the agreement of laboratory analytes, physiological variables, newer instruments and other devices.B-A methodR advocates the wind of a scatter p parcel out, where the coercive oddment mingled with the diametrical measurements is plot on y-axis against the mingy of two methods on x-axis. The SD of varietys amid paired measurements is and then used to construct 95% limits of agreement (as 1.96 SD). The 95% of differences surrounded by paired measurements are expected to lie mingled with these upper and lower LOA. The conclusions on agreement and interchangeability of two methods are then made found upon the width of these LOA in comparison to a priori outlined clinical criteriaR. The plot also enables the researcher to visually assess the b ias, information scatter and the affinity between magnitude of difference and size of measurement. Often in biological systems data scatter and the magnitude of differences increases proportionally to the size of the measurement (hetero-scedastic distribution). Bland and Altman recommended the logarithmic or percentageage transformation of data in lineament of hetero-scedastic distribution and then constructing B-A plot with transformed dataR instead of determinate absolute difference plot.Contrary to conventional statistical hypothesis testing, the output of B-A analysis consists of bias and LOA, both of which are estimatesR. The estimates have inherent risk of consume error and hence the authors suggested calculation of confidence interval (CI) of bias and LOA. The method also advocated the collection of data in replicates. Replicates are defined as two or more measurements on the same individual by the same method, taken in identical conditions. Replicates enable the compar ison of the agreement between the two methods with the agreement each method has to itself (repeatability) R B-A also advocated for try on size calculations on in method comparison studiesR.Despite its restraint and frequent use in clinical laboratory research, the B-A method is non properly interpreted and describe in medical literature. Studies Rconducted a decennary ago highlighted poor reporting standards of B-A method, however there is paucity of current information on the same. Furthermore, uniform statistical reporting of results not only increases the generalizability of results, but also facilitates the inclusion of studies in systemic reviews and meta-analysis. Hence the work out of study was to review the current reporting standards of B-A method in laboratory research in medical literature.Material and methods-Three researchers (VC, RB, and SK) participated in this study. all told researchers were qualified health professionals. VC and SK had previous experience of publishing laboratory research R with use of B- A agreement analysis.Eligibility criteria- Studies which tested agreement of laboratory analytes with continuous measurements, as per B-A methodology were include.Literature search- A thorough search of PUBMED, MEDLINE and GOOGLE educatee was conducted for studies create in years 2012 and 2013. The search strings used to search potential studies were Agreement analysis AND/OR Bland Altman analysis (MeSH) and Laboratory analytes and clinical biochemistry (MeSH). Included studies were evaluated according to Bland and Altman methodology on a predesigned checklist. The studies were evaluated for following 8 items (1.) Measures of repeatability (2.) Representation and correct definition of LOA (3.) Correct way of x-axis on BA plot (4.) Reporting of CI of LOA (5.) Comparison of limits of agreement with a priori defined clinical criteria (6.) Evaluation of mould of family relationship between difference (y-axis) and total (x-axis) (7.) Use of logarithmic or percentage innovation of data in representative of heteroscedastic relationship between the difference and norm (8.) Sample size calculations. Each item on the checklist was rated as Yesor No. We also save the data on use of other statistical methods for testing of agreement. However, we did not practice detailed evaluation of include studies for other statistical methods of agreement.To ensure accurate data retrieval, each included study was evaluated twice by one author (VC) and data recorded on predesigned checklist. Opinion was taken from second author (SKK) in case of confusion arising during data extraction. We compared the results of our study with 3 similar surveys done earlier.Results-A total of 156 studies were screened for potential inclusion in the study. A total of 50 studies, were retrieved and included in the final study. The 38% of included studies were published in journals of various streams of internal medicine, while 30%, 26% and 6% we re published in journals of laboratory medicine, emergency medicine, anaesthesia respectively. Results of survey and its comparison to tierce previous studies are as shown in Table-1.The other statistical methods used in addition to B-A plot in included studies were correlation coefficient (70%), Deming Regression(14%), firing Bablok regression (14%), linear regression (24%), Lins Concordance (8%), Sensitivity specificity analysis (16%), Interclass correlation coefficient (6%), Grid error plot (10%), Critchley polar plots (2%).Discussion-Use of B-A for method comparison has increased in recent years with some of authors development it for analysing agreement. The original paper on agreement analysis by B-AR is among one of most cited statistical publication, with more than 34000 citations. Although claimed as a method which is simpler to perform and interpret, the method is often used and interpreted without proper understanding. Review by Berthelsen et alR in 2006 and earlier s tudiesR demonstrated disappointing reporting of B-A analyses, in anaesthesiology literature. Williamson et alR proposed a method of meta-analysis of method comparison studies, however authors also highlighted the problem of non-uniform reporting of studies. RTwomey et al R suggested use of method hierarchy for selection of x-axis and advocated use of gilded standard method as x-axis in B-A plot. However Bland and Altman statistically proved that use of any single method instead of average of two methods as x-axis is misguided and leads to misinterpretationR. Results of our study suggest that 94% of studies reported x-axis correctly, which is almost similar to results of earlier studies conducted by Mantha et al (94%) R and Dewitt et al (87%) R. although most method comparison computer softwares (analyse it, Graphpad Prism, EP evaluator) automatically select x-axis as mean of two methods, errors in selection of x-axis are still noticed.The 95% LOA were correctly defined and pinch ed in 94 %( 47) of included studies. Further among 47 studies with correct definition of LOA, the 3 studies interpreted LOA wrongly concluding goodish agreement because 95 % of differences were present in-between upper and lower LOA. The 95 % LOA are in-fact drawn so as to contain 95% of differences between them. It is not LOA per se, but width of these LOA in comparison to a priori defined clinical criteria that conclusions regarding agreements can be made. The decision on acceptable differences between two methods is primarily clinical rather than statistical. Earlier studies by Dewitte et al Rand Mantha et alR had shown that comparison with pre-defined clinical criteria was missing in 90% of studies. Total 74 % of authors in our study commented on agreement on basis of predefined clinical criteria which represents a significant improvement in reporting standards. The specifications for clinical acceptance criteria of laboratory analytes have been provided as by Ricos et alR, CLS IR, and West guard QCR. Alternatively a Delphi survey (expert opinion) can be done to determine acceptable limits earlier instituting study.The CI limits of LOA were reported in only 6% of included studies in our study. The LOA are estimates and reporting LOA without CI is equivalent to reporting a exemplification mean without its CI. The CI limits Ludbrook et al represent the range within which a single, new, manifestation taken from the same population would be expected to lie. Although strongly recommended by B-AR, and subsequently proved by a simulation study conducted by Hamilton et alR, the statistical reporting of CI of LOA has remained poor (Mantha et al-2.6%) R.Although recommended by B-A method, the pattern of relationship between difference and wider absorption range is rarely evaluatedR. Drawing difference plot with parallel LOA in datasets with heteroscedastic scatter makes LOA wider in lower concentration range and narrower in higher concentration range thus touchi ng validity of interpretation. R Bland and Altman Rproposed logarithmic transformation of data with heteroscedasticy and then constructing difference plot against average of two methods using log transformed data. For meaning(prenominal) understanding of LOA, they suggested back-transformation (antilog) of the log transformed data. AlternativelyR plot of ratios of two methods or percent difference can be plotted against average of two methods for simpler interpretation. regeneration of data usually renders the scatter of differences as uniform (Homoscedastic). Twomey et alR recommended the drawing up of funnel shaped or V shaped LOA instead of classical parallel LOA in data sets with heteroscedastic scatter. Another option is breaking the data into smaller subsets and then analysing these subsets with absolute difference plot to make conclusions. Twomey et al We sight that only 28 % of studies made an attempt at evaluation of pattern of scatter. Rest of authors did not comment on pattern thus alter the validity of results.Another important problem noticed was lack of assessment of repeatability (38%), a practice that has not shown any substantial improvement Table-1. Conclusions drawn from studies without repeatability assessment are homogeneously to be uncertain. Assessment of errors of the two methods (repeatability) enables the verbal expression of the worst-case acceptable LOA. R With poor repeatability of one or both methods, the agreement between the two methods is bound to be unacceptable. RSample size calculations were done in only 15 studies. Lack of power and sample size analysis reduces validity of results. Different researchers have proposed sample size calculation for method comparison studies using BayesianR, regressionR, or concordance R approach. However Stockl et alR proposed an approach incorporating CI of LOA and predefined error limits in B-A plot. The approach is simple and allows for visual interpretation of appropriate sample size , as the classical B-A plot provides for agreement.Despite a lot of research on B-A method in field of statistics, the uptake of the method in medical research has been slow. While efforts are on in statistical confederacy for use of modifications of B-A plot in special situations like repeated measure studiesR or using bar charts in B-A plots with express value rangesR, unfortunately reporting standards of classical B-A method among medical community are unacceptable. Guidelines Reporting reliability and Agreement Studies (GRRAS) were published as a guide to appropriate reporting of reliability and agreement studies. We found unsatisfactory reporting of B-A analysis in our study.