Measurement reliability has been expressed in relative and absolute measures [ 39, 40]. In the current study, the reliability term was used as a hypernym for expressions defining various aspects of measurement uncertainty [ 39, 40], although some authors have used agreement term for this purpose [ 41] or have understood reliability in a narrower sense [ 4, 5, 41]. Cook JR, Baker NA, Cham R, Hale E, Redfern MS: Measurements of wrist and finger postures: a comparison of goniometric and motion capture techniques. J Appl Biomech. 2007, 23: 70-78. Burr N, Pratt AL, Stott D: Inter-rater and intra-rater reliability when measuring interphalangeal joints: comparison between three hand-held goniometers. Physiotherapy. 2003, 89: 641-652. 10.1016/S0031-9406(05)60097-1.

The inter-rater and intra-rater reliability of the electrogoniometer is higher than the universal goniometer but challenging to apply in patients' clinical evaluation, hence used more often for research purposes [1]

For continuous variables, the most common measure of relative reliability is intraclass correlation coefficient (ICC) accompanied by appropriate analysis of variance (ANOVA) [ 40]. Differently from the previous studies, which used the popular models of ICCs described by Shrout and Fleiss [ 42], the current investigation employed concurrent assessment of reliability proposed by Eliasziw et al. [ 43]. Unlike calculating the traditional ICCs, the method of concurrent assessment allows simultaneous estimation of intra-rater and inter-rater reliability along with the hypothesis testing in cases when multiple raters evaluate multiple subjects and perform more than one measurement per subject. In respect to the traditional models, the concurrent methodology has been cited as a more advantageous approach [ 44]. Maxwell SE, Delaney HD: Designing Experiments and Analyzing Data: A Model Comparison Perspective. 2004, Mahwah, NJ: Lawrence Erlbaum Associates, 2nd

De Vet HC, Terwee CB, Knol DL, Bouter LM: When to use agreement versus reliability measures. J Clin Epidemiol. 2006, 59: 1033-1039. 10.1016/j.jclinepi.2005.10.015. Exploratory data analysis included obtaining descriptive statistics, searching for outliers, and assessing the normality of distribution of the appropriate data sets by means of Shapiro-Wilk tests and the analysis of histograms and Q-Q plots. Analysis of the study parts A Groth GN, VanDeven KM, Phillips EC, Ehretsman RL: Goniometry of the proximal and distal interphalangeal joints, Part II: placement preferences, interrater reliability, and concurrent validity. J Hand Ther. 2001, 14: 23-29. 10.1016/S0894-1130(01)80021-1. All the blanks with the recorded angles of the joints were scanned. The scanned diagrams were magnified, and their angles were measured to the nearest degree by the same researcher with ImageJ program. Each diagram was measured at least twice without reference to the previous results. If the results of the two computerized measurements were different, the diagram was remeasured again. If 2 identical measurements were not obtained, mean of the measurements was found and rounded off to the nearest degree. To assess intra-rater and inter-rater reliability of the latter procedure, two invited medical students remeasured 48 randomly chosen scanned diagrams. Computerized evaluation instead of a simple use of a traditional protractor was chosen to equalize varying sizes of the hand drawn diagrams and to avoid errors of hand-done measurements. Independence of observationsHayen A, Dennis RJ, Finch CF: Determining the intra- and inter-observer reliability of screening tools used in sports injury research. J Sci Med Sport. 2007, 10: 201-210. 10.1016/j.jsams.2006.09.002. The results of all the analytical approaches support the suggestion that both goniometers can be used interchangeably. Significance of goniometer effect apparent from some of the 2x10 ANOVAs should be interpreted in conjunction with significant goniometer by rater interaction, indicating that the performance of the instrument tended to be depended on which the rater was using it. The small magnitudes of the differences between the reliability estimates of the techniques were not convincing enough to state disparity of the methods. In the three cases of failure to reject the null hypothesis for paper goniometer alone, the LLs of 95% one-sided L-L CIs levels above 0.7 can still be considered as an acceptable level of reliability for non-professional novice raters. Interchangeability of goniometers was also demonstrated by the binomial tests, which involved assessment of the inter-goniometer ≤ 5-degree agreement. It is notable, that the results of the proportion analysis echo the outcomes of parametric assessments indicating that the measurement consistency was rater and joint dependent. Parity of the goniometers was further shown by the results of the study parts B, indicating that data collected with both instruments can be similarly interpreted in an exploration of simulated change in joint range of motion over time. Decrease in the reliability estimates in the second stage of the study part A may be due to the weariness of the participants. To find whether the try-angle guides significantly changed the observed angles of the PIP joint, multiple Wilcoxon signed-rank tests with Bonferroni correction were performed for each rater-instrument-position-subposition data set in respect to the baseline joint angles obtained by using the smallest standard angles. Then the standard differences between the angles of the appropriate try-angles (i.e., between the standard angles) were calculated in respect of the smallest standard angles. Next, the lowest significant standard differences were found between the smallest standard angles and the angles of the try-angles, application of which produced significant changes in the observed PIP joint angles (Additional file 6). The lowest significant standard differences were compared with each other and with the corresponding values of the MDC derived from the SEMs of the study parts A. Analysis of reliability of the diagram evaluation Chiu HY, Su FC, Wang ST, Hsu HY: The motion analysis system and goniometry of the finger joints. J Hand Surg Br. 1998, 23: 788-791. 10.1016/S0266-7681(98)80098-3. Lewis E, Fors L, Tharion WJ: Interrater and intrarater reliability of finger goniometric measurements. Am J Occup Ther. 2010, 64: 555-561. 10.5014/ajot.2010.09028.

The repeated measures 2x2x10 ANOVAs revealed that the main effect of goniometer was insignificant. The main effect of trial was significant for the MCP joint in imitated extension in study part I-A and in all study part II-A subgroups. The main effect of rater was significant for the MCP joint in study part I-A and in all study part II-A subgroups. Trial by rater interaction effect was observed in all the subgroups except for that of the DIP joint in position of imitated flexion. Goniometer by trial interaction was observed only in the DIP joint extension subgroup of the study part II-A. The 2x10 ANOVAs showed that goniometer and rater effects were insignificant in approximately half of the trial-position-joint data sets. Most of the two-way ANOVAs resulted in significant goniometer by rater interaction. Insignificance of all effects was observed only in the study part I-A, for the first trial measurements of the DIP joint and for the second trial measurements of the PIP joint in flexion. Macdermid JC, Fox E, Richards RS, Roth JH: Validity of pulp-to-palm distance as a measure of finger flexion. J Hand Surg Br. 2001, 26: 432-435. 10.1054/jhsb.2001.0612.The finding of this study that the measurements of the distal interphalangeal joint are relatively less consistent corresponds to the results of the earlier research [ 2, 26, 33, 37]. This phenomenon may be associated with the stabilization difficulty of the less powered interphalangeal joints and limited phalangeal length available for the alignment of the arms of goniometers. The results of the current study also corroborate the observations of the other researchers that intra-rater reliability is better than inter-rater reliability [ 2, 6, 7, 23, 25, 26, 28, 33]. Power analysis prior to the study was performed for a 2-sample t test for noninferiority, which calculated a sample size of 13 subjects based on a mean difference of 5°, a standard deviation of 10% of the expected measurement, α of 0.05, and a power of 0.80. Five degrees of difference is the accepted standard error in manual goniometry of the hand. 8, 9 For this study, the authors elected to include a larger sample size (n = 50). With varying size options, the EZ Read Jamar Goniometer is excellent for measuring patients of all sizes. The transparent plastic with clear marking is easy to read and encourages accurate measurements. Goniometers of different sizes are needed for measuring a variety of body parts. Use to measure fingers, wrists, elbows, knees, and ankles. EZ Read Jamar Goniometers are available in sizes that range from 6” to 12.5.” This range matches the needs of all healthcare professionals in clinical environments. Jamar Bruton A, Conway JH, Holgate ST: Reliability: What is it and how is it measured?. Physiotherapy. 2000, 86: 94-99. 10.1016/S0031-9406(05)61211-4. Record measurements correctly (both active and passive range of motion should be measured and recorded respectively). [1]