according to a survey conducted by the japanese physical therapy association of its 59,328 
 members , between december 20 , 2009 to january 31 , 2010 , hemiplegia ( 13.6% ) , pain ( 13.2% ) , 
 muscle weakness ( 13.0% ) , and limited range of motion ( rom ; 10.6% ) are the most common 
 impairments treated in physical therapy1 . although improving rom is a common therapeutic goal of physical therapy , effective treatment 
 of rom restrictions is often difficult . application of evidence - based methods and reliable 
 measurement of rom are essential components of an effective therapeutic intervention to 
 increase rom . the importance of measuring rom has led to the development of several rom measurement 
 methods , including visual assessment scales2 ; the universal goniometer3 ; the electrogoniometer4 ; digital imaging5 ; 
 three - dimensional motion analysis systems6 ; and , recently , the use of smartphone - based goniometers7 . each of these measurement techniques has 
 advantages and drawbacks in particular applications in practice and research . in clinical 
 practice the 
 information obtained from universal goniometers is used to quantify the extent of 
 restriction in joint rom , to inform intervention selection and application , to assess the 
 effects of an intervention , and to confirm the progress of physical therapy treatment . therefore , understanding the validity and reliability of measurements of rom obtained using 
 a universal goniometer is highly relevant to physical therapy practice and has been 
 investigated by a number of researchers . currier8 defines validity as  the degree 
 to which an instrument measures what it is purported to measure  and ,  the extent to which 
 the measurement fulfills its purpose  . in other words , the validity of a measurement 
 instrument refers to the degree to which it can reproduce the validity is broadly divided into four types : face validity , 
 content validity , criterion - related validity , and construct validity . previous studies have 
 supported the face , content and criterion - related validity of rom measurements using a 
 universal goniometer9,10,11 . of these , criterion 
 validity is of particular importance , establishing the measurement obtained against an 
 accepted gold standard . gogia et al.12 evaluated measurements of knee joint positions , between 0 
 to 120 of 30 subjects , which were made by two physical therapists using a universal 
 goniometer , and compared them with radiographs of the joint position obtained immediately 
 after the measurement . the goniometric measurements correlated with the radiographic angles , 
 with correlation coefficients of 0.97 and 0.98 , respectively , for the two therapists . based 
 on their results , goglia et al . considered knee rom measurements to be valid . a similar 
 comparison of knee rom measures obtained using a universal goniometer and radiographs was 
 completed by enwemeka13 . in enwemeka s 
 experiment , a universal goniometer was used to position the right knee of 10 participants at 
 angles of 0 , 15 , 30 , 45 , 60 , and 90 , and radiographs of the end - point position were 
 obtained . for knee joint flexion angles between 30 and 90 , the difference between 
 goniometric and radiographic measurements ranged between 0.52 and 3.81 , a difference which 
 was not significant . on the other hand , for knee joint flexion angles between 0 and 15 , 
 the difference between goniometric and radiographic measurements increased to 4.59 , which 
 was significant . therefore , according to these results , the criterion validity of rom 
 obtained by universal goniometer varies depending on the rom , with a high level of agreement 
 between goniometric and radiographic measurements for knee joint angles between 30 and 90 , 
 and low for angles 15. reliability is defined as the consistency of measurements or of an individual s performance 
 in a test15 , 16 . baumgarter17 
 further divided reliability into two types , relative reliability and absolute reliability . relative reliability is defined as the degree to which individuals maintain their position 
 in a sample with repeated measurements . this type of reliability is often evaluated using 
 pearson s product - moment correlation coefficient or the intra - class correlation coefficient . absolute reliability is defined as the degree to which repeated measurements vary among 
 individuals . this type of reliability is represented in actual units of measurement or as 
 measurement ratios . measurement error is quantified using repeated measures using absolute 
 reliability indices , such as the bland - altman method18 , standard error of measurement , and the minimum detectable change 
 ( mdc)19 , 20 . the bland - altman method is a useful method as it allows 
 visualization and statistical evaluation of the presence or absence of systematic bias in 
 measurements . standard error of measurement represents the minimum level of change that 
 demonstrates true improvement in a group , while the mdc represents the minimum level of 
 change that represents true improvement for an individual21 , 22 . previous studies 
 evaluating the reliability of rom measurements have mostly addressed relative reliability , 
 with intra - tester reliability being higher than inter - tester reliability23 , 24 . however , very few studies have examined the absolute reliability of 
 rom measurements . lenssen et al.25 used 
 the bland - altman method and the mdc to evaluate the absolute reliability of knee rom 
 measurement of 30 hospitalized patients , on day 3 or 4 following total knee arthroplasty , as 
 measured by two physical therapists using a universal goniometer . they reported a fair level 
 of agreement between testers , establishing differences in rom of < 8 as being 
 indistinguishable from measurement error . in clinical settings , physical therapists routinely use a change in rom from pre- to 
 post - intervention to assess the effects of the intervention . however , with limited evidence 
 regarding the error in rom measured using a universal goniometer , it is not known to what 
 degree these measurements actually reflect a change in rom due to the intervention . also , 
 although previous studies have examined the effects of factors such as age26 , gender27 , and body mass index28 on rom measurement , there has been no investigation of the effects 
 of the proficiency level of the tester on error in measurement of rom using a universal 
 goniometer . this issue is highly relevant when it is considered that rom measures obtained 
 by physical therapists with different levels of experience are used to evaluate change 
 related to an intervention in practice . the 
 first was to use the bland - altman method to evaluate the type and extent of error in the 
 measurement of rom using a universal goniometer . the second was to evaluate the effect of 
 the proficiency level on the magnitude of the measurement error . understanding of the type 
 and magnitude of measurement error using a universal goniometer will enable more accurate 
 interpretation of measurements and improve the accuracy of clinical reasoning . moreover , 
 findings could assist educators in the implementation of strategies to improve students 
 proficiency in rom measurement techniques . the participants were 45 physical therapy students recruited from a university , and 21 
 physical therapists recruited from a general hospital . students were recruited from 
 different years of study in a physical therapy program , with the distribution as follows : 15 
 second - year students , 15 third - year students , and 15 fourth - year students . at the 
 university , the students learn rom measurement within the first two months of their second 
 year ( april or may ) . therefore , the lapse of time from learning the basic techniques of rom 
 measurement to participation in our study was approximately 9 months for second - year 
 students , 21 months for third - year students and 33 months for fourth - year students . the 
 student group was further differentiated by their clinical experience , with only fourth year 
 students having completed all their clinical education . among the 21 physical therapist 
 recruited from the hospital , 7 were in their first year of clinical experience , 8 in their 
 second year and 6 in their third year . their training institution , university or vocational 
 school , was not taken into account . overall in our study group , the lapse of time from 
 learning of basic techniques of rom measurement ranged between 1  year , for second year 
 students , to 6  years , for physical therapists in their third year of clinical practice . all 
 participants performed rom measurements on the same volunteer , a healthy young male with no 
 past history of orthopedic disorders of his right knee . the methods and procedures for our study were approved by the mejiro university 
 institutional review board ( approval number : 15 - 013 ) . all participants , and the volunteer , 
 received a full explanation of the study and provided their informed consent . prior to conducting the full study , we completed a pilot study to confirm the accuracy of 
 knee rom measurements obtained using an electrogoniometer ( sg150 , biometrics ltd . , uk ) , 
 which was used as the criterion value for the evaluation of the measurement error of the 
 universal goniometer . a standardized procedure was used to position the electrogoniometer 
 for the recording of knee joint rom positions . the electrogoniometer was attached to the 
 right leg using double - sided tape , with the knee flexed to 60. the proximal point of 
 attachment was localized 1  cm from the lateral epicondyle of the femur , along a line 
 connecting the greater trochanter and the lateral epicondyle of the femur . the distal point 
 of attachment was localized 1  cm from the head of the fibula , along a line connecting the 
 head of the fibula and the lateral malleolus . the bony landmarks used as a reference for the 
 localization of the electrogoniometer were identified by palpation and marked . a thin string 
 was attached with tape between both pairs of landmarks ( i.e. , greater trochanter and lateral 
 epicondyle of the femur ; head of the fibula and lateral malleolus ) . the thin string was used 
 as a guide to attach the electrogoniometer . once the electrogoniometer was placed and 
 secured , an elastic wrap was used to prevent slipping of the electrogoniometer during 
 measurements , as well as to hide its position from the participants performing measurements 
 using a universal goniometer . reflective markers were then placed over the bony landmarks , 
 namely the greater trochanter , lateral epicondyle of the femur , head of the fibula , and 
 lateral malleolus to visualize their positions on digital images captured obtained by a 
 two - camera system ( b - cam , dkh , japan ) . passive knee rom was measured by one experimenter , 
 from full extension to maximum flexion , with the experimenter taking care to maintain the 
 knee motion in the sagittal plane , avoiding adduction / abduction and internal / external 
 rotation motions of the hip as much as possible . the measurement was recorded by the 
 two - camera system with the signals between the cameras and the electrogoniometer 
 synchronized using a trigger switch . the knee joint position data obtained from the 
 electrogoniometer and the imaging data captured by the cameras were analyzed using a motion 
 analysis system ( frame - dias v , dkh , japan ) . for the imaging data , the knee joint angle was 
 defined as the angle formed by the line connecting the greater trochanter and the lateral 
 epicondyle and the line connecting the head of the fibula and the lateral malleolus . agreement between the imaging and electrogoniometer data was evaluated by simple linear 
 regression , using the imaging data as the dependent variable and the electrogoniometer data 
 as the independent variable . the level of agreement between the electrogoniometer and 
 imaging data was high at knee flexion angles of 20 to 90 
 ( y=0.960x , r=0.998 , p<0.001 ) . each participant performed two consecutive measurements of passive 
 knee flexion rom , and the limb was returned to its original position between measurements . for all measurements , the electrogoniometer was attached by one experimenter , using the 
 standardized procedures , with its position hidden from participants by the elastic wrap . the 
 electrogoniometer was connected to a data logger ( ph-7010 , dkh , japan ) , providing a real 
 time display of measurements to the experimenter , with signals saved at a sampling frequency 
 of 100  hz for off - line analysis . audio feedback of threshold knee positions of 60 and 75 
 was provided to the volunteer through stereo earphones . an audio signal was provided when 
 knee rom exceeded 60 and disappeared when the rom exceeded 75. the volunteer used the 
 audio feedback to simulate knee flexion restrictions . on the first measurement trial , upon 
 hearing the audio feedback ( i.e. , 60 of knee flexion ) , the volunteer would say that the 
 knee will not bend any further  and resist the force being applied to flex the knee by the 
 participant . in the second measurement trial , the volunteer would say the same and resist 
 motion at the cessation of the audio feedback ( i.e. , 75 of knee flexion ) . these scenarios 
 were used to simulate a pre- to post - intervention change in rom , as might be found in 
 practice . this goniometer had a 
 handle 30  cm in length and angle marks with 1 increments . the measurement landmarks were 
 the greater trochanter , the lateral epicondyle of the femur , the head of the fibula , and the 
 lateral malleolus . the angle formed by the line connecting the greater trochanter and the 
 lateral epicondyle of the femur and the line connecting the head of the fibula and the 
 lateral malleolus was measured by the participants in 1 increments . measurements were 
 performed using participants usual technique , with no instructions 
 provided regarding confirmation of localization of landmarks by palpation , the technique for 
 passively flexing the knee , or the method used to position the goniometer on the leg . as 
 soon as the participants completed their measurement , they were instructed to announce 
  done  and to report the measurement to the experimenter . event trigger ( is3 , dkh , japan ) input into the data logger . this event marker was used to synchronize the signal from the electrogoniometer with the 
 end - position measured using the universal goniometer . the angle provided by the 
 electrogoniometer was used as the criterion reference value , with the measurement error of 
 the universal goniometer quantified as the difference between the measure stated by the 
 participant and the reference value recorded using the electrogoniometer . the time required 
 to complete the measurement was the time from the start of the trial , including palpation of 
 bony landmarks , to the time when the participant announced  done  . the following variables were used in the analysis : level of proficiency , defined as the 
 number of years since receiving basic instruction in goniometry measurement ; measurement 
 error ; and measurement time . the means and standard deviations ( sd ) of the measurement error 
 and measurement time were calculated for the proficiency level ( 16 years ) . reproducibility 
 of the end - point of knee rom by the volunteer was evaluated for the first ( 60 ) and second 
 ( 75 ) trials by calculating the mean and sd of the values recorded by the electrogoniometer . the absolute measurement error was calculated as the difference between the rom measure of 
 the electrogoniometer and the measure reported by the participants . the mean , sd and 95% 
 confidence interval ( ci ) of the absolute error was calculated for each proficiency level . split - plot analysis of variance ( anova ) was used to evaluate the effect of proficiency level 
 on the absolute measurement error and measurement time as dependent variables . a 
 bland - altman analysis was performed to evaluate the presence or absence of systematic bias 
 in the rom measurements obtained using a universal goniometer . the differences between the 
 measurements obtained with the electrogoniometer and the universal goniometer were plotted 
 along the y - axis , with the mean of both measurements plotted along the 
 x - axis . the mean difference ( md ) , sd of the md ( sddif ) , and 
 95% ci of the md the magnitude of 
 the random error in measurement was evaluated by calculating the mdc at the 95% ci level 
 ( mdc95 ) as follows : mdc95=1.96 sddif . all statistical 
 analyses were performed using ibm spss statistics software ( ver . 23 ) . the mean  sd measurement values and measurement times , as a function of proficiency level , 
 are reported in table 1table 1.means and standard deviations of measurement values and measurement times of the 
 electrogoniometer and the universal goniometer by proficiency levelproficiency levelfirst measurementsecond measurementeg ( deg)ug ( deg)mt ( s)eg ( deg)ug ( deg)mt ( s)students1(n=15)64.5  5.167.1  6.951.7  22.785.3  4.687.5  5.934.3  9.32(n=15)61.2  6.762.1  11.057.3  24.788.3  5.486.6  6.742.8  14.63(n=15)63.7  8.265.0  9.854.1  22.984.5  6.383.9  6.741.5  16.9physical therapists4(n=7)63.1  4.962.7  3.951.6  25.882.7  4.580.9  3.040.6  15.75(n=8)64.1  4.964.8  5.243.7  12.878.7  2.677.4  3.933.6  13.56(n=6)65.3  4.264.5  5.548.3  16.881.0  5.181.3  4.937.0 22.3values are reported as the mean  sd ; eg : electrogoniometer ; ug : universal 
 goniometer ; mt : measurement time . the mean  sd of the first and second reference positions measured by the 
 electrogoniometer were 63.4  6.1 and 84.3  5.8 , respectively , indicative of a good 
 reproducibility of the reference angles across trials . the mean , sd and 95%ci of the 
 difference between the criterion value of the electrogoniometer and the measurement using 
 the universal goniometers are reported , as a function of proficiency level , in table 2table 2.mean , standard deviation and 95% ci of the absolute measurement error 
 ( deg)proficiency levelfirst measurement second measurementaveragemean  sd95% cimean  sd95% cimean  sd95% cistudents1(n=15)6.8  4.34.49.26.7  3.54.78.76.8  3.95.58.02(n=15)5.6  3.43.77.54.9  4.12.67.15.3  3.84.06.53(n=15)4.2  2.32.95.54.1  2.03.05.24.2  2.12.95.4physical therapists4(n=7)4.3  1.13.35.33.3  2.11.45.33.8  2.42.15.65(n=8)2.0  1.50.73.22.6  1.71.23.92.3  1.00.63.96(n=6)2.2  1.50.63.71.1 overall , both absolute error and variability in measurement decreased as the 
 proficiency level increased . split - plot anova , with absolute measurement error used as the 
 dependent variable and proficiency level ( 16 ) and measurement order ( first or second 
 measurement ) as factors , identified a main effect of proficiency level 
 ( f5,60=6.517 , p<0.001 , p=0.352 ) on measurement error , 
 with no significant effect of order of measurement ( f1,60=0.756 , p=0.388 , 
 p=0.012 ) or proficiency level  measurement order interaction 
 ( f5,60=0.256 , p=0.935 , p=0.021 ) . multiple comparisons 
 for proficiency levels , using the bonferroni method , identified significant differences in 
 rom measurements between the following proficiency levels : 1 and 5  years ( p=0.001 ) ; 1 and 
 6  years ( p<0.001 ) ; and 2 and 6  years ( p=0.033 ) . values are reported as the mean  sd ; eg : electrogoniometer ; ug : universal 
 goniometer ; mt : measurement time 95% ci : 95% confidence interval split - plot anova , with measurement time used as the dependent variable and proficiency 
 level ( 16 ) and measurement order ( first or second measurement ) as factors , identified a 
 significant main effect of measurement order ( f1,60=29.735 , p<0.001 , 
 p=0.331 ) on measurement time , with no significant effect of 
 proficiency level ( f5,60=0.651 , p=0.662 , p=0.051 ) or 
 proficiency level measurement order interaction ( f5,60=0.267 , p=0.929 , 
 p=0.022 ) . the bland - altman plot used to evaluate systematic bias 1.bland-altman plot of the measurement values of the electrogoniometer ( eg ) and the 
 universal goniometer ( ug)the solid line shows the mean difference between the 2 
 measurement methods and the 2 dotted lines indicate the  1.96 standard deviation ; 
 x - axis , mean angle of both measurement instruments ( ug and eg ) ; 
 y - axis , the difference between the angle as measured by ug and as 
 measured by eg .. the mean absolute difference in measurement was low at 0.4 ( 95% ci , 1.7 to 1.0 ) 
 and , therefore , there was no evidence of fixed error in rom measurements . simple linear 
 regression analysis also showed there was no evidence of proportional bias in measurement , 
 with a regression coefficient of nearly zero , and the regression line was not significant : 
 y=0.018x  0.94 ; r=0.037 ; p=0.67 . bland - altman plot of the measurement values of the electrogoniometer ( eg ) and the 
 universal goniometer ( ug)the solid line shows the mean difference between the 2 
 measurement methods and the 2 dotted lines indicate the  1.96 standard deviation ; 
 x - axis , mean angle of both measurement instruments ( ug and eg ) ; 
 y - axis , the difference between the angle as measured by ug and as 
 measured by eg . the bland - altman analysis performed as a function of proficiency level confirmed the 
 absence of systematic bias on measurements obtained using the universal goniometer , 
 regardless of proficiency level ( table 
 3table 3.bland-altman analysis of measurement errorproficiency levelmd  sddif ( deg)fixed error ( deg)proportional biasmdc95 ( deg)95%ciregression coefficientstudents1(n=15)2.4  7.50.45.20.03714.72(n=15)0.4  6.52.82.10.04612.83(n=15)0.3  4.71.52.10.0209.3physical therapists4(n=7)1.1 4.23.51.30.288.35(n=8)0.3  2.81.71.10.205.56(n=6)0.2  2.11.51.10.374.1md : mean difference ; sddif : standard deviation of the mean difference ; 95% 
 ci : 95% confidence interval ; mdc95 : minimal detectable change at the 95% 
 confidence level ) . the mdc95 values , however , did decrease as proficiency level 
 increased , indicating a lowering in the random error of measurement as the proficiency level 
 increased . md : mean difference ; sddif : standard deviation of the mean difference ; 95% 
 ci : 95% confidence interval ; mdc95 : minimal detectable change at the 95% 
 confidence level in this study , the bland - altman method was used to quantitatively determine the type and 
 magnitude of error in rom measurements made using a universal goniometer and to evaluate the 
 effects of learning on identified measurement error . while systematic error was not found in 
 the measurements , the magnitude of the random error did decrease with increasing level of 
 proficiency . the accuracy of the electrogoniometer 
 measurements used as criterion values was first established , and it showed that 
 electrogoniometer measurements were reliable for the rom of knee flexion between 20 and 
 90. piriyaprasarth et al.29 previously 
 reported the standard error of measurement with an electrogoniometer , placed by the same 
 tester across repeated trials , to be < 1.7. kettelkamp et al.30 proposed that errors in electrogoniometer measurements 
 resulted from misalignment of the electrogoniometer with the anatomical axis of the knee 
 joint and/or due to slippage during operation . therefore , in the preset study , all 
 measurements were performed on a single healthy young adult , with the electrogoniometer 
 positioned and secured by a single experimenter . in order to minimize any misalignment of 
 the electrogoniometer with the anatomical axis of the knee joint , reference lines connecting 
 the greater trochanter and the lateral epicondyle of the femur was used , as well as the head 
 of the fibula and the lateral malleolus , to guide the experimenter to reproducibly attach 
 the electrogoniometer to the right lower limb . in order to prevent slippage of the 
 electrogoniometer during flexion motions of the knee , the electrogoniometer was attached to 
 the skin with double - sided tape , and then fixed with surgical tape and an elastic wrap . any 
 errors due to positioning and slippage would have manifested as systematic bias in 
 measurement . no evidence of such systematic bias was found ( fig . 1 , table 3 ) . 
 therefore , we are confident that differences between measurements obtained using the 
 universal goniometer and the criterion reference , obtained using an electrogoniometer , were 
  true errors . anova identified a significant main effect of proficiency level on absolute measurement 
 error , with error decreasing as a function of increased proficiency . the proficiency level 
 was defined the number of years since receiving basic instruction in goniometry measurement . therefore , participants with a higher proficiency level were inferred to have performed 
 goniometric measures a greater number of times . from the results , it can be inferred that 
 practice significantly improves the accuracy of rom measurements . previous studies of skill 
 acquisition have demonstrated that the amount of practice is an important factor in skill 
 acquisition , both for accuracy and consistency in performance31 , 32 . although decrease in 
 performance time is also an important indicator of skill acquisition , an effect of 
 proficiency level on measurement time was not found . we postulate that this finding can be 
 explained within the previously described phenomenon of a speed - accuracy trade - off33 . in the present study , speed would be 
 the measurement time and  accuracy would be the measurement error . participants in the 
 present study were not given any instructions regarding the measurement time , therefore , it 
 is likely that participants focused on being as accurate as possible . we recognize that the 
 physical therapists recruited from the general hospital for this study only had a maximum of 
 three years of clinical experience . it is possible that with more years of clinical 
 experience , physical therapists may become better at measuring rom accurately , without 
 sacrificing time . our bland - altman analysis did not identify evidence of systematic bias in measurements 
 using the universal goniometer , with no fixed or proportional error detected . therefore , 
 measures of rom using a universal goniometer were only influenced by random errors . mdc95 was calculated as an index of absolute reliability , which represents the 
 minimum change that demonstrates a change in rom less than the 
 mdc95 can not be differentiated from random error in measurement . therefore , in 
 practice , it is impossible to determine whether pre- to post - physical therapy intervention 
 changes in rom that are within the mdc95 range represent a mdc95 was found to be influenced by the level of proficiency , with the 
 mdc95 value of 14.7 at 1  year decreasing to 4.1 after three years of clinical 
 experience . at an mdc95 level of 14.7 , changes in rom < 15 can not be 
 differentiated from measurement error , thus making it impossible to identify small , but 
 possibly relevant , changes in rom . in contrast , the mdc95 value of 4.1 of the 
 more experienced therapists indicates that changes 5 can be interpreted as true changes 
 in rom , which would increase the sensitivity of rom measurements to the effects of physical 
 therapy intervention . the effect of random error in rom measures obtained by a novice therapist can be reduced by 
 using the mean value of multiple measurements , an approach that has been reported in 
 previous studies to improve the reliability of rom measurements34 , 35 . for the 
 measurement of knee and elbow rom , rothstein et al.34 reported that inter - tester reliability obtained from the mean of 
 two measurements was slightly better than inter - tester reliability obtained from a single 
 measurement . thus , if the only type of error involved in rom measurements is random in 
 nature , then averaging the means of multiple measurements can cancel out random error and 
 consequently yield more accurate values . this is a strategy that might benefit novice 
 therapists and learners and improve the reliability of the interpretations of their 
 measurements in practice , with the number of measurements reducing as the magnitude of 
 random error decreases . moreover , increasing the amount of practice ( i.e. , the number of 
 measurements performed ) could be an effective teaching strategy for improving the accuracy 
 of rom measurements using a universal goniometer , with high repetition enhancing motor 
 learning and skill acquisition36 , 37 . however , during practice of 
 rom measurement , there is no effective feedback provided to the learning regarding the 
 accuracy of measurement . we speculate that development of a feedback device based on 
 electrogoniometry might promote better acquisition of rom measurement skill . therefore , 
 going forward , we would like to focus on developing such feedback devices and evaluate their 
 usefulness in learning and practice . the limitations of the present study need to be acknowledged in the interpretation of 
 results . foremost , the results are only valid within the context of rom measurement of right 
 knee flexion using a metal universal goniometer . although evaluation was limited to the 
 joint that is most commonly evaluated in practice , it is important to note that previous 
 studies have reported the reliability of rom measurements to be influenced by the joint 
 being measured23 , 24 and the device used38 , 39 . in addition , the participants in the 
 present study were limited to students from a single university and physical therapists 
 working at a single general hospital , therefore , caution should be exercised when 
 generalizing the results to other groups of students and therapists . in order to overcome 
 these limitations and enable more accurate interpretation of measurements , a variety of 
 joints must be examined and participants in future studies must include students from other 
 universities and physical therapists working at other institutions .
[ purpose ] the aims of this study were to evaluate the type and extent of error in the 
 measurement of range of motion and to evaluate the effect of evaluators proficiency level 
 on measurement error . [ subjects and methods ] the participants were 45 university students , 
 in different years of their physical therapy education , and 21 physical therapists , with 
 up to three years of clinical experience in a general hospital . 
 range of motion of right 
 knee flexion was measured using a universal goniometer . 
 an electrogoniometer attached to 
 the right knee and hidden from the view of the participants was used as the criterion to 
 evaluate error in measurement using the universal goniometer . 
 the type and magnitude of 
 error were evaluated using the bland - altman method . 
 [ results ] measurements with the 
 universal goniometer were not influenced by systematic bias . 
 the extent of random error in 
 measurement decreased as the level of proficiency and clinical experience increased . 
 [ conclusion ] measurements of range of motion obtained using a universal goniometer are 
 influenced by random errors , with the extent of error being a factor of proficiency . 
 therefore , increasing the amount of practice would be an effective strategy for improving 
 the accuracy of range of motion measurements .