Critical appraisal of the CLSI guideline EP09c "measurement procedure comparison and bias estimation using patient samples".

BACKGROUND: In laboratory setting evaluating the agreement between two measurement methods is a very frequent practice. Unfortunately, the guidelines to refer to are not free from criticisms from a statistical methodological point of view. We reviewed the Clinical and Laboratory Standards Institute guideline EP09c, 3rd ed. pointing out some drawbacks and some aspects that have not been well defined, leaving situations of uncertainty and/or of excessive subjectivity in the judgement. CONTENT: We have stressed the need of having replicates to estimate the systematic and the proportional biases of the measurement methods to be compared. Indeed, unequal variance of the two measurement methods gives a slope and intercept of the regression between the difference and the mean of the two values of the measurement methods to be compared that can be absolutely calculated from their means, their variances and their correlation coefficient. So, it is not possible to disentangle true from spurious biases. For laboratory professionals we have developed a worked exemplification of an agreement assessment. SUMMARY: We have stressed the need of other approaches than the classic Bland and Altman method to calculate the systematic and proportional biases of two measurement methods compared for their agreement in a study with replicates.

Vertical Center-of-Mass Braking and Motor Performance during Gait Initiation in Young Healthy Adults, Elderly Healthy Adults, and Patients with Parkinson's Disease: A Comparison of Force-Plate and Markerless Motion Capture Systems.

BACKGROUND: This study tested the agreement between a markerless motion capture system and force-plate system ("gold standard") to quantify stability control and motor performance during gait initiation. METHODS: Healthy adults (young and elderly) and patients with Parkinson's disease performed gait initiation series at spontaneous and maximal velocity on a system of two force-plates placed in series while being filmed by a markerless motion capture system. Signals from both systems were used to compute the peak of forward center-of-mass velocity (indicator of motor performance) and the braking index (indicator of stability control). RESULTS: Descriptive statistics indicated that both systems detected between-group differences and velocity effects similarly, while a Bland-Altman plot analysis showed that mean biases of both biomechanical indicators were virtually zero in all groups and conditions. Bayes factor 01 indicated strong (braking index) and moderate (motor performance) evidence that both systems provided equivalent values. However, a trial-by-trial analysis of Bland-Altman plots revealed the possibility of differences >10% between the two systems. CONCLUSION: Although non-negligible differences do occur, a markerless motion capture system appears to be as efficient as a force-plate system in detecting Parkinson's disease and velocity condition effects on the braking index and motor performance.

Mass Spectrometry-Based Evaluation of the Bland-Altman Approach: Review, Discussion, and Proposal.

Reliable quantification in biological systems of endogenous low- and high-molecular substances, drugs and their metabolites, is of particular importance in diagnosis and therapy, and in basic and clinical research. The analytical characteristics of analytical approaches have many differences, including in core features such as accuracy, precision, specificity, and limits of detection (LOD) and quantitation (LOQ). Several different mathematic approaches were developed and used for the comparison of two analytical methods applied to the same chemical compound in the same biological sample. Generally, comparisons of results obtained by two analytical methods yields different quantitative results. Yet, which mathematical approach gives the most reliable results? Which mathematical approach is best suited to demonstrate agreement between the methods, or the superiority of an analytical method A over analytical method B? The simplest and most frequently used method of comparison is the linear regression analysis of data observed by method A (y) and the data observed by method B (x): y = α + ßx. In 1986, Bland and Altman indicated that linear regression analysis, notably the use of the correlation coefficient, is inappropriate for method-comparison. Instead, Bland and Altman have suggested an alternative approach, which is generally known as the Bland-Altman approach. Originally, this method of comparison was applied in medicine, for instance, to measure blood pressure by two devices. The Bland-Altman approach was rapidly adapted in analytical chemistry and in clinical chemistry. To date, the approach suggested by Bland-Altman approach is one of the most widely used mathematical approaches for method-comparison. With about 37,000 citations, the original paper published in the journal The Lancet in 1986 is among the most frequently cited scientific papers in this area to date. Nevertheless, the Bland-Altman approach has not been really set on a quantitative basis. No criteria have been proposed thus far, in which the Bland-Altman approach can form the basis on which analytical agreement or the better analytical method can be demonstrated. In this article, the Bland-Altman approach is re-valuated from a quantitative bioanalytical perspective, and an attempt is made to propose acceptance criteria. For this purpose, different analytical methods were compared with Gold Standard analytical methods based on mass spectrometry (MS) and tandem mass spectrometry (MS/MS), i.e., GC-MS, GC-MS/MS, LC-MS and LC-MS/MS. Other chromatographic and non-chromatographic methods were also considered. The results for several different endogenous substances, including nitrate, anandamide, homoarginine, creatinine and malondialdehyde in human plasma, serum and urine are discussed. In addition to the Bland-Altman approach, linear regression analysis and the Oldham-Eksborg method-comparison approaches were used and compared. Special emphasis was given to the relation of difference and mean in the Bland-Altman approach. Currently available guidelines for method validation were also considered. Acceptance criteria for method agreement were proposed, including the slope and correlation coefficient in linear regression, and the coefficient of variation for the percentage difference in the Bland-Altman and Oldham-Eksborg approaches.

Validity and reliability of three-dimensional costal cartilage imaging for donor-site assessment and clinical application in microtia reconstruction patients: A prospective study of 22 cases.

OBJECTIVES: This study assesses the ability to reconstruct costal cartilage images by using three-dimensional visualisation software (Mimics) based on semi-automated segmentation algorithm and to investigate its reliability and validity with an anthropometric analysis. DESIGN: Observational prospective study. SETTING: Plastic surgery department of a tertiary hospital. PARTICIPANTS: Twenty-two microtia patients who underwent autologous ear reconstruction. MAIN OUTCOME MEASURES: Preoperative thoracic computed tomography data were processed to Mimics software for three-dimensional costal cartilage imaging. The length, width, thickness and volume of the 9th costal cartilages were calculated from these images and compared with the direct measurements (DM) obtained intraoperatively. RESULTS: The intra-examiner reliability and inter-examiner reliability were high in terms of all four measurements (intraclass correlation coefficients, ICC: 0.876-0.984). There were no significant differences between image-based anthropometry and DM in the linear measurements except for the volume (P < .05). The mean volume calculation error of Mimics was -0.08 ± 0.13 mL. No correlation was found between the anthropometric variables and the absolute errors (P > .05). Furthermore, Bland-Altman plots were used to evaluate the agreement between the two methods. CONCLUSIONS: Despite a very small error was found in volume calculation, Mimics software was accurate and reliable in linear calculation. Three-dimensional costal cartilage imaging was found to be an efficient tool for morphological evaluation of costal cartilages. We believe that with the application of individualised cartilage models based on three-dimensional printing, the use of customised ear framework carving will be practicable in surgical training.

Comparison of two color-difference formulas using the Bland-Altman approach based on gingiva color space.

The objectives of this study were to determine the relationship between the results provided by the classical CIELab (ΔEab*) and the CIEDE2000 (ΔE00) formulas and the gingival color space using the Bland and Altman limits of agreement, to use this relationship to establish the equivalences between the gingival color thresholds of perceptibility of both formulas, and to evaluate whether the relationship between ΔEab* and ΔE00 is modified depending on the axis in which the changes occur. The means of the L*, a*, and b* coordinates of the 21 gingiva porcelain samples (Heraceram, Heraeus Kulzer Mitsui Chemical Groups) were used and the differences in color were calculated in 210 pairs of samples using the CIELab (ΔE*ab) and CIEDE2000 (ΔE00) color-difference formulas. The results obtained with these formulas were compared and the limits of agreement after a logarithmic transformation of the data were obtained. The relationship between both formulas was ln ΔE00 = - 0.22 + ln ΔEab*. The results obtained with the CIELab formula were between 1.01 (95% confidence interval 0.98-1.03) and 1.54 (95% confidence interval 1.52-1.59) times higher than those obtained with the CIEDE200 formula. In the gingiva color space, the scale factor between the CIEDE2000 and CIELab values changes from 0.63 to 1.02, such that providing an accurate scale factor between both values proves difficult. The pairs with the highest ratio were those where the difference in color was mainly due to changes in lightness, whereas the pairs with the smallest ratio were those where the difference in color was mainly due to changes in the blue-yellow or green-red axes.

Reliability of Eustachian tube function measurements in a hypobaric and hyperbaric pressure chamber.

OBJECTIVES: Measurement of the Eustachian tube (ET) function is a challenge. The demand for a precise and meaningful diagnostic tool increases-especially because more and more operative therapies are being offered without objective evidence. The measurement of the ET function by continuous impedance recording in a pressure chamber is an established method, although the reliability of the measurements is still unclear. METHODS: Twenty-five participants (50 ears) were exposed to phases of compression and decompression in a hypo- and hyperbaric pressure chamber. The ET function reflecting parameters-ET opening pressure (ETOP), ET opening duration (ETOD) and ET opening frequency (ETOF)-were determined under exactly the same preconditions three times in a row. The intraclass correlation coefficient (ICC) and Bland and Altman plot were used to assess test-retest reliability. RESULTS: ICCs revealed a high correlation for ETOP and ETOF in phases of decompression (passive equalisation) as well as ETOD and ETOP in phases of compression (active induced equalisation). Very high correlation could be shown for ETOD in decompression and ETOF in compression phases. The Bland and Altman graphs could show that measurements provide results within a 95 % confidence interval in compression and decompression phases. CONCLUSIONS: We conclude that measurements in a pressure chamber are a very valuable tool in terms of estimating the ET opening and closing function. Measurements show some variance comparing participants, but provide reliable results within a 95 % confidence interval in retest. This study is the basis for enabling efficacy measurements of ET treatment modalities.

Improved interpretation of studies comparing methods of dietary assessment: combining equivalence testing with the limits of agreement.

The aim of this study was to demonstrate the use of testing for equivalence in combination with the Bland and Altman method when assessing agreement between two dietary methods. A sample data set, with eighty subjects simulated from previously published studies, was used to compare a FFQ with three 24 h recalls (24HR) for assessing dietary I intake. The mean I intake using the FFQ was 126·51 (sd 54·06) µg and using the three 24HR was 124·23 (sd 48·62) µg. The bias was -2·28 (sd 43·93) µg with a 90% CI 10·46, 5·89 µg. The limits of agreement (LOA) were -88·38, 83·82 µg. Four equivalence regions were compared. Using the conventional 10 % equivalence range, the methods are shown to be equivalent both by using the CI (-12·4, 12·4 µg) and the two one-sided tests approach (lower t=-2·99 (79 df), P=0·002; upper t=2·06 (79 df), P=0·021). However, we make a case that clinical decision making should be used to set the equivalence limits, and for nutrients where there are potential issues with deficiency or toxicity stricter criteria may be needed. If the equivalence region is lowered to ±5 µg, or ± 10 µg, these methods are no longer equivalent, and if a wider limit of ±15 µg is accepted they are again equivalent. Using equivalence testing, acceptable agreement must be assessed a priori and justified; this makes the process of defining agreement more transparent and results easier to interpret than relying on the LOA alone.

Comparison of Urinary Total Proteins by Four Different Methods.

The total proteins in human urine have been compared by sulfosalicylic acid, sulfosalicylic acid with sodium sulphate and trichloroacetic acid methods with pyrogallol red molybdate method as there are no studies found quantifying imprecision and bias components. Fresh urine of 36 patients was analyzed by four methods. Imprecision and inaccuracy were determined by repeated analysis and method comparison studies using correlation plots, Bland and Altman, and Passing and Bablok regression analyses respectively. The coefficient of variation was 5.07 % for pyrogallol red molybdate; 6.84 % for sulfosalicylic acid; 3.97 % for sulfosalicylic acid with sodium sulphate and 5.93 % for trichloroacetic acid methods. Bland and Altman analysis showed a bias of 5.8, 1.7 and -5.4 for pyrogallol red molybdate versus sulfosalicylic acid, sulfosalicylic acid with sodium sulphate and trichloroacetic acid methods respectively. Passing and Bablok regression revealed a constant bias for pyrogallol red molybdate versus all turbidimetric methods but a proportional bias only with trichloroacetic acid method. Sulfosalicylic acid with sodium sulphate method is preferred to sulfosalicylic acid and trichloroacetic acid methods.

To have value, comparisons of high-throughput phenotyping methods need statistical tests of bias and variance.

The gap between genomics and phenomics is narrowing. The rate at which it is narrowing, however, is being slowed by improper statistical comparison of methods. Quantification using Pearson's correlation coefficient (r) is commonly used to assess method quality, but it is an often misleading statistic for this purpose as it is unable to provide information about the relative quality of two methods. Using r can both erroneously discount methods that are inherently more precise and validate methods that are less accurate. These errors occur because of logical flaws inherent in the use of r when comparing methods, not as a problem of limited sample size or the unavoidable possibility of a type I error. A popular alternative to using r is to measure the limits of agreement (LOA). However both r and LOA fail to identify which instrument is more or less variable than the other and can lead to incorrect conclusions about method quality. An alternative approach, comparing variances of methods, requires repeated measurements of the same subject, but avoids incorrect conclusions. Variance comparison is arguably the most important component of method validation and, thus, when repeated measurements are possible, variance comparison provides considerable value to these studies. Statistical tests to compare variances presented here are well established, easy to interpret and ubiquitously available. The widespread use of r has potentially led to numerous incorrect conclusions about method quality, hampering development, and the approach described here would be useful to advance high throughput phenotyping methods but can also extend into any branch of science. The adoption of the statistical techniques outlined in this paper will help speed the adoption of new high throughput phenotyping techniques by indicating when one should reject a new method, outright replace an old method or conditionally use a new method.

Comparison Between Actigraphy Records and Parental Reports of Child's Sleep.

Given the impact of sleep in several domains of a child's development, the comparison between actigraphy and parental questionnaires is of great importance in preschool-aged children, an understudied group. While parental reports tend to overestimate sleep duration, actigraphy boosts the frequency of night-waking's. Our primary goal was to compare actigraphy data and parental reports (Children's Sleep Habits Questionnaire, CSHQ), regarding bedtime, wake-up time, sleep duration, and wake after sleep onset (WASO), using the Bland-Altman technique. Forty-six children, age 3-6 years, and their parents participated. Results suggest that, despite existing associations between sleep schedule variables measured by both methods (from r = 0.57 regarding bedtime at weekends to r = 0.86 regarding wake-up time during the week, ps), differences between them were significant and agreements were weak, with parents overestimating bedtimes and wake-up times in relation to actigraphy. Differences between actigraphy and CSHQ were ± 52 min for weekly bedtime, ± 38 min for weekly wake-up time, ±159 min for total sleep time, and ± 62 min for WASO, indicating unsatisfactory agreement between methods. Correlations between actigraphy data and CSHQ dimensions are also explored. Our study contributes to the knowledge of the characteristics of each instrument, along with their tendency to overestimate and underestimate certain sleep parameters. We conclude that a complementary use of both instruments would better inform clinical practice and research on a child's sleep.

Interrater agreement on behavioral executive function measures in adolescents with Attention Deficit Hyperactivity Disorder.

Though most children with Attention Deficit Hyperactivity Disorder (ADHD) show difficulties in behavioral measures of executive functions (EF), few studies have examined interrater agreement in these measures. OBJECTIVE: To analyze the agreement between parents, teachers and self-reports of behavioral EF in adolescents with ADHD and controls. METHOD: A sample of 118 adolescents (75 with ADHD and 43 controls) was rated by parents, teachers and the adolescents themselves using the Comprehensive Executive Function Inventory. The intraclass correlation coefficient (ICC) and Bland and Altman methods were used to evaluate agreement. RESULTS: The ICC between parents, teachers and self-report was poor or moderate in the group with ADHD; in the control group the agreement was fair to good. The Bland and Altman graphs show that, in the control group, most of the scores are below to the clinical cut-off point, while in the group with ADHD they are above. CONCLUSIONS: Agreement between all raters was low. Parents, teachers and adolescents agreed on the absence of deficits in behavioral EF in the control group, and on the presence of deficits in the group with ADHD, although they did not agree on the frequency of these deficits.

ANTECEDENTES/OBJETIVO: Aunque muchos adolescentes con Trastorno por Déficit de Atención con Hiperactividad (TDAH) muestran dificultades en las funciones ejecutivas (FE) conductuales, pocos estudios han analizado el acuerdo entre informantes en estas medidas. Objetivo: Analizar el acuerdo entre informantes en la valoración de FE conductuales en adolescentes con TDAH y controles. Método: Ciento dieciocho adolescentes (75 con TDAH y 43 controles) fueron evaluados con el Comprehensive Executive Function Inventory por padres, maestros y autoinforme. Se utilizó el coeficiente de correlación intraclase (ICC), y el método de Bland y Altman para evaluar el acuerdo entre informantes. Resultados: El ICC varía entre bajo y moderado en el grupo con TDAH, y entre moderado y bueno en el grupo control. Los gráficos de Bland y Altman muestran que, en el grupo control, la mayoría de las puntuaciones se sitúan por debajo del punto de corte clínico, mientras que en el grupo con TDAH están por encima del punto de corte. Conclusiones: El acuerdo entre informantes es bajo. Padres, maestros y adolescentes coinciden en la ausencia de déficits en las FE conductuales en el grupo control y en la presencia de déficits en el grupo con TDAH, aunque no coinciden en la frecuencia de estos déficits.

Assessment of the Agreement between Cerebral Hemodynamic Indices Quantified Using Dynamic Susceptibility Contrast and Dynamic Contrast-enhanced Perfusion Magnetic Resonance Imagings.

BACKGROUND: Brain tumor is one of the most common tumors. A successful treatment might be achieved with an early identification. Pathological investigation as the gold standard method for tumor identification has some limitations. Noninvasive assessment of tumor specifications may be possible using perfusion-weighted magnetic resonance imaging (MRI). Cerebral blood volume (CBV) and cerebral blood flow (CBF) could be calculated based on dynamic contrast-enhanced MRI (DCE-MRI) in addition to dynamic susceptibility contrast MRI (DSC-MRI) modality. Each category of the cerebral hemodynamic and permeability indices revealed the specific tumor characteristics and their collection could help for better identification of the tumor. Some mathematical methods were developed to determine both cerebral hemodynamic and permeability indices based on a single-dose DCE perfusion MRI. There are only a few studies available on the comparison of DSC- and DCE-derived cerebral hemodynamic indices such as CBF and CBV. AIM: The objective of the study was to validate first-pass perfusion parameters derived from T1-based DCE method in comparison to the routine T2*-based DSC protocol. MATERIALS AND METHODS: Twenty-nine patients with brain tumor underwent DCE- and DSC-MRIs to evaluate the agreement between DSC- and DCE-derived cerebral hemodynamic parameters. Agreement between DSC- and DCE-derived cerebral hemodynamic indices was determined using the statistical method described by Bland and Altman. The reliability between DSC- and DCE-derived cerebral hemodynamic indices was measured using the intraclass correlation analysis. RESULTS: The achieved magnitudes for DCE-derived CBV (gray matter [GM]: 5.01 ± 1.40 mL/100 g vs. white matter [WM]: 1.84 ± 0.74 mL/100 g) and DCE-derived CBF (GM: 60.53 ± 12.70 mL/100 g/min vs. WM: 32.00 ± 6.00 mL/100 g/min) were in good agreement with other studies. The intraclass correlation coefficients showed that the cerebral hemodynamic indices could accurately be estimated based on the DCE-MRI using a single-compartment model (>0.87), and DCE-derived cerebral hemodynamic indices are significantly similar to the magnitudes achieved based on the DSC-MRI (P < 0.001). Furthermore, an acceptable agreement was observed between DSC- and DCE-derived cerebral hemodynamic indices. CONCLUSION: Based on the measurement of the cerebral hemodynamic and blood-brain barrier permeability using DCE-MRI, a more comprehensive collection of the physiological parameters cloud be achieved for tumor evaluations.

Quantification of vehicle fleet PM10 particulate matter emission factors from exhaust and non-exhaust sources using tunnel measurement techniques.

Road tunnels act like large laboratories; they provide an excellent environment to quantify atmospheric particles emission factors from exhaust and non-exhaust sources due to their known boundary conditions. Current work compares the High Volume, Dichotomous Stacked Filter Unit and Partisol Air Sampler for coarse, PM10 and PM2.5 particle concentration measurement and found that they do not differ significantly (p = 95%). PM2.5 fraction contributes 66% of PM10 proportions and significantly influenced by traffic (turbulence) and meteorological conditions. Mass emission factors for PM10 varies from 21.3 ± 1.9 to 28.8 ± 3.4 mg/vkm and composed of Motorcycle (0.0003-0.001 mg/vkm), Cars (26.1-33.4 mg/vkm), LDVs (2.4-3.0 mg/vkm), HDVs (2.2-2.8 mg/vkm) and Buses (0.1 mg/vkm). Based on Lawrence et al. (2013), source apportionment modelling, the PM10 emission of brake wear (3.8-4.4 mg/vkm), petrol exhaust (3.9-4.5 mg/vkm), diesel exhaust (7.2-8.3 mg/vkm), re-suspension (9-10.4 mg/vkm), road surface wear (3.9-4.5 mg/vkm), and unexplained (7.2 mg/vkm) were also calculated. The current study determined that the combined non-exhaust fleet PM10 emission factor (16.7-19.3 mg/vkm) are higher than the combined exhaust emission factor (11.1-12.8 mg/vkm). Thus, highlight the significance of non-exhaust emissions and the need for legislation and abatement strategies to reduce their contributions to ambient PM concentrations.

Interchangeability of Electrocardiography and Blood Pressure Measurement for Determining Heart Rate and Heart Rate Variability in Free-Moving Domestic Pigs in Various Behavioral Contexts.

This study assessed the interchangeability between heart rate (HR) and heart rate variability (HRV) measures derived from a series of interbeat intervals (IBIs) recorded via electrocardiogram (ECG) and intra-arterial blood pressure (BP) in various behavioral contexts. Five minutes of simultaneously recorded IBIs from ECG and BP signals in 11 female domestic pigs during resting, feeding, and active behavior were analyzed. Comparisons were made for measures of HR, the standard deviation of IBIs, and the root mean of the squared distances of subsequent IBIs derived from ECG and BP signals for each behavior category using statistical procedures with different explanatory power [linear regression, intraclass correlation coefficient (ICC), Bland and Altman plots, and analysis of variance (ANOVA)]. Linear regression showed a strong relationship for HR during all behaviors and for HRV during resting. Excellent ICCs [lower 95% confidence intervals (CI) >0.75] and narrow limits of agreement in all behavior categories were found for HR. ICCs for HRV reached the critical lower 95% CI value of 0.75 only during resting. Using Bland and Altman plots, HRV agreement was unacceptable for all of the behavior categories. ANOVA showed significant differences between the methods in terms of HRV. BP systematically overestimated HRV compared with ECG. Our findings reveal that HR data recorded via BP agree well those recorded using ECG independently of the activity of the subject, whereas ECG and BP cannot be used interchangeably in the context of HRV in free-moving domestic pigs.

Comparative Analysis of Urinary Total Proteins by Bicinchoninic Acid and Pyrogallol Red Molybdate Methods.

BACKGROUND: The concentration of total proteins in urine is a good index of renal function, but its determination is found to be unreliable. The pyrogallol red molybdate (PRM) method for urine total proteins is being widely used in most of the hospitals because of its high sensitivity, better precision and its practicability. Bicinchoninic acid method (BCA) is also used for protein estimation and there have been no studies comparing this method with the PRM method in human urine samples. BCA method overestimates the urinary protein concentration in the presence of interfering substances. After removing the interfering substances present in the human urine samples the results of BCA method were compared with the PRM method. AIM: The purpose of the study is to identify whether the results of urine total proteins by BCA method are comparable to PRM method and can be used as an alternative to the PRM method. SETTING AND DESIGN: This is a cross-sectional study done on fresh urine specimens from the hospital laboratory, covering a wide range of protein concentrations. MATERIAL AND METHODS: Fresh urine specimens covering a wide range of protein concentrations (urine dipstick: nil, trace, 1+, 2+ and ≥ 3+) of 36 patients were analysed by both the methods. STATISTICAL ANALYSIS: Imprecision was determined by repeated analysis study and Inaccuracy was assessed by comparing the results of the patient's urine samples by both the methods using correlation plots, Bland and Altman, and Passing and Bablok regression analyses. RESULTS: The coefficient of variation and mean (SD) for the BCA method were 4.6% and 799.1 (882.5) mg/L and for the PRM method were 5.1% and 802.1 (911.9) mg/L. The Pearson correlation coefficient, r was 0.93 (p < 0.0001). Method agreement studies showed no significant constant and proportional bias between both the methods. CONCLUSION: In urine which is subjected to removal of interfering substances, the BCA results are comparable to PRM method.

Test-retest reliability of three dimensional gait analysis: including a novel approach to visualising agreement of gait cycle waveforms with Bland and Altman plots.

BACKGROUND/AIM: Estimating the measurement error (reliability) of three dimensional gait analysis (3DGA) is crucial to interpretation of gait data. The purpose of this study was to investigate the intra-rater reliability of 3DGA and apply a novel method of visualising reliability of gait cycle waveforms. METHODS: A test re-test design was employed. A convenience sample of 30 healthy adults (18F; 12 M: mean age 30 ± 6.8 years) participated. Subjects walked along a 10 m walkway at their preferred gait speed and 3DGA data were collected using a VICON(®) 3DGA system. Testing was performed by the same investigator on two separate days within two weeks. Data from 10 trials were averaged and analysed. ANALYSIS: The intraclass correlation coefficient (ICC), the standard error of measurement (SEM), minimal detectable change (MDC) and limits of agreement were calculated for kinetic and kinematic data. Bland and Altman plots were applied to gait cycle waveforms. RESULTS: Spatio-temporal parameters such as cadence, step length, velocity, step time and step width were highly repeatable generating ICC's of 0.90 and above and low SEM/MDC. Range of joint movement across the gait cycle was generally more reliable than either minimum or maximum values and higher ICCs were obtained for movement in the sagittal plane. For kinematic data the standard error of measurement was low (≤ 5) for the majority of parameters. Transverse plane measurements showed poor reliability with lowest ICC's. ICCs for kinetic data ranged from 0.51 to 0.81. CONCLUSIONS: Reliability of 3DGA has been estimated for our gait laboratory. Bland and Altman plots of gait cycle waveforms provide a useful addition to reliability analysis.

Translation of oswestry disability index into Tamil with cross cultural adaptation and evaluation of reliability and validity(§).

STUDY DESIGN: Prospective longitudinal validation study. OBJECTIVE: To translate and cross-culturally adapt the Oswestry Disability Index (ODI) to the Tamil language (ODI-T), and to evaluate its reliability and construct validity. SUMMARY OF BACKGROUND DATA: ODI is widely used as a disease specific questionnaire in back pain patients to evaluate pain and disability. A thorough literature search revealed that the Tamil version of the ODI has not been previously published. METHODS: The ODI was translated and cross-culturally adapted to the Tamil language according to established guidelines. 30 subjects (16 women and 14 men) with a mean age of 42.7 years (S.D. 13.6; Range 22 - 69) with low back pain were recruited to assess the psychometric properties of the ODI-T Questionnaire. Patients completed the ODI-T, Roland-Morris disability questionnaire (RMDQ), VAS-pain and VAS-disability at baseline and 24-72 hours from the baseline visit. RESULTS: The ODI-T displayed a high degree of internal consistency, with a Cronbach's alpha of 0.92. The test-retest reliability was high (n=30) with an ICC of 0.92 (95% CI, 0.84 to 0.96) and a mean re-test difference of 2.6 points lower on re-test. The ODI-T scores exhibited a strong correlation with the RMDQ scores (r = 0.82) p<0.01, VAS-P (r = 0.78) p<0.01 and VAS-D (r = 0.81) p<0.01. Moderate to low correlations were observed between the ODI-T and lumbar ROM (r = -0.27 to -0.53). All the hypotheses that were constructed apriori were supported. CONCLUSION: The Tamil version of the ODI Questionnaire is a valid and reliable tool that can be used to measure subjective outcomes of pain and disability in Tamil speaking patients with low back pain.

Testing agreement between a new method and the gold standard-how do we test?

Data analysis can be the most challenging aspect of a research study. Having been taught statistical techniques that tend to be based on finding significant differences or significant relationships, difficulties arise when trying to determine if a newly developed method is equally as good as the established method (the gold standard). Testing for significant differences is rigorous and it would be rare for researchers to report significant differences without using an appropriate statistical test. Testing for agreement is assessed with far less rigour. Analysis of papers in this journal suggests that testing for agreement is an area that could be improved by a better understanding of statistical methods by biomechanics researchers. This perspectives paper focusses on informing the reader about the assessment of agreement between two methods.

Electrolytes assessed by point-of-care testing - Are the values comparable with results obtained from the central laboratory?

BACKGROUND AND AIMS: When dealing with very sick patients, the speed and accuracy of tests to detect metabolic derangements is very important. We evaluated if there was agreement between whole blood electrolytes measured by a point-of-care device and serum electrolytes measured using indirect ion-selective electrodes. MATERIALS AND METHODS: In this prospective study, electrolytes were analyzed in 44 paired samples drawn from critically ill patients. Whole blood electrolytes were analyzed using a point-of-care blood gas analyzer and serum electrolytes were analyzed in the central laboratory on samples transported through a rapid transit pneumatic system. Agreement was summarized by the mean difference with 95% limits of agreement (LOA) and Lin's concordance correlation (p(c)). RESULTS: There was a significant difference in the mean (±standard deviation) sodium value between whole blood and serum samples (135.8 ± 5.7 mmol/L vs. 139.9 ± 5.4 mmol/L, P < 0.001), with the agreement being modest (p(c) = 0.71; mean difference -4.0; 95% LOA -8.78 to 0.65). Although the agreement between whole blood and serum potassium was good (p(c) = 0.96), and the average difference small (-0.3; 95% LOA -0.72 to 0.13), individual differences were clinically significant, particularly at lower potassium values. For potassium values <3.0 mmol/L, the concordance was low (p(c) = 0.53) and the LOA was wide (1.0 to -0.13). The concordance for potassium was good (p(c) = 0.96) for values ≥3.0 (mean difference -0.2; 95% LOA -0.48 to 0.06). CONCLUSIONS: Clinicians should be aware of the difference between whole blood and serum electrolytes, particularly when urgent samples are tested at point of care and routine follow-up electrolytes are sent to the central laboratory. A correction factor needs to be determined at each center.

Análisis de concordancia entre el dosaje de inmunoglobulinas y la fracción gamma del proteinograma sérico / Analysis of agreement between the dosage of immunoglobulins and gamma fraction of serum protein electrophoresis / Análise de concordancia entre a dosagem de imunoglobulinas e a fragao gamma do proteinograma sérico

En este trabajo se proponen dos criterios que evalúan el acuerdo existente entre densitometría y nefelometría, en la evaluación de los niveles de inmunoglobulinas en suero, basados en la propia población de pacientes y su posible aplicación en un algoritmo de autoverificación. Se construyó la variable Diferencia GAMgamma = Suma Igs - gamma; se efectuó el análisis según el método de Bland y Altman. Se estimó el IC95% empleando como referencia una cohorte de 497 pacientes concurrentes al laboratorio del Hospital A. Posadas en octubre y noviembre de 2011 y que tenían un dosaje de inmunoglobulinas G, A y M normal para población adulta. Estos resultados fueron contrastados con 2 poblaciones: a) 977 sujetos concurrentes en el mismo período y b) 111 pacientes con presencia de componente monoclonal (CM). En la población de referencia el IC95% Diferencia (mg/dL) fue de 115-653 y el DE para los límites ± 21 mg/dL. Utilizando los criterios Valores de referencia seguido por Diferencia se obtuvieron los siguientes resultados: Población de pacientes: 470/977 (48,1%) pasaron las dos alarmas y serán autovalidados. Población con CM: el 75,6% dio al menos una alarma. No obstante, si bien se puede considerar aceptable esta sensibilidad, hubo 27 CM que pasaron las dos alarmas. Se concluye que luego de una inspección visual previa, casi el 50% de los resultados serán autovalidados.

Two criteria are proposed to evaluate the agreement between densitometry and nephelometry of serum immunoglobulin level, based on own patient population and its possible application in a self-validation algorithm. A difference GAMgamma = Sum Igs -gamma variable was constructed; analysis was performed according to the Bland and Altman method. CI 95% was estimated using as reference a cohort of 497 patients attending Posadas Hospital's laboratory in October and November 2011 who had a normal dosage of G, A and M immunoglobulins for an adult population. These results were compared with two populations: a) 977 patients attending the hospital in the same period and b) 111 patients with monoclonal component (MC). In the reference population, the CI 95% Difference (mg/dL) was 115-653 and the limits were ± 21 mg/dL. Using Reference Values criteria followed by Difference, the following results were obtained: in the patient population, 470/977 (48.1%) passed both alarms and will be validated. In the MC population, 75.6% gave at least one alarm. However, although this may be considered acceptable sensitivity, there were 27 MC who passed both alarms. It can be concluded that after a visual inspection, almost 50% of the results will be self-validated.

Neste trabalho sáo propostos dois critérios que avaliam o acordo existente entre densitometria e nefelometría, na avaliagáo dos níveis de imunoglobulinas em soro, com base na pròpria populagáo de doentes e a sua possível aplicagáo num algoritmo de autovalidagáo. Foi construida a variável Diferenga GAMgamma = Soma Igs - gama, a análise foi realizada de acordo com o método de Bland & Altman. IC95% foi estimada utilizando-se como referencia uma coorte com 497 doentes concorrentes ao laboratòrio do hospital Posadas em outubro e novembro de 2011 e que tinham uma dosagem normal de imunoglobulinas G, A e M para populagáo adulta. Estes resultados foram comparados com duas populagdes-. a) 977 doentes concorrentes no mesmo período e b) 111 doentes com presenga de componente monoclonal (CM). Na populagáo de referencia, IC95% Diferenga (mg/dL): (115-653) e o DE para os limites ± 21 mg/dL foram os resultados. Utilizando os critérios Valores de Referencia seguidos de Diferenga foram obtidos os seguintes resultados: A populagáo de doentes de 470/977 (48,1%) passou os dois alarmes e seráo autovalidados. A populagáo com CM que deu pelo menos um alarme foi de 75,6%. No entanto, embora esta sensibilidade possa ser considerada aceitável, houve 27 CM que passaram os dois alarmes. A conclusáo é que depois de uma inspegáo visual prévia, cerca de 50% dos resultados seráo autovalidados.