Intra-observer Measurement Error Research Articles

THE REPRODUCIBILITY OF CORONAL PLANE KNEE ALIGNMENT MEASUREMENTS ON LONG-LEG STANDING RADIOGRAPHS AND COMPARISON WITH NON-WEIGHTBEARING MAKO CT

Identifying and restoring alignment is a primary aim of total knee arthroplasty (TKA). In the coronal plane, the pre-pathological hip knee angle can be predicted using an arithmetic method (aHKA) by measuring the medial proximal tibial angle (MPTA) and lateral distal femoral angle (aHKA=MPTA - LDFA). The aHKA is shown to be predictive of coronal alignment prior to the onset of osteoarthritis; a useful guide when considering a non-mechanically aligned TKA. The aim of this study is to investigate the intra- and inter-observer accuracy of aHKA measurements on long leg standing radiographs (LLR) and preoperative Mako CT planning scans (CTs).Sixty-eight patients who underwent TKA from 2020-2021 with pre-operative LLR and CTs were included. Three observers (Surgeon, Fellow, Registrar) measured the LDFA and MPTA on LLR and CT independently on three separate occasions, to determine aHKA. Statistical analysis was undertaken with Bland-Altman test and coefficient of repeatability.An average intra-observer measurement error of 3.5° on LLR and 1.73° on CTs for MPTA was detected. Inter-observer errors were 2.74° on LLR and 1.28° on CTs. For LDFA, average intra-observer measurement error was 2.93° on LLR and 2.3° on CTs, with inter-observer errors of 2.31° on LLR and 1.92° on CTs. Average aHKA intra-observer error was 4.8° on LLR and 2.82° on CTs. Inter-observer error of 3.56° for LLR and 2.0° on CTs was measured.The aHKA is reproducible on both LLR and CT. CT measurements are more reproducible both between and within observers. The difference between measurements using LLR and CT is small and hence these two can be considered interchangeable. CT may obviate the need for LLRs and may overcome difficulties associated with positioning, rotation, body habitus and flexion contractures when assessing coronal alignment.

Quantification of epicardial fat using 3D cine Dixon MRI

BackgroundThere is an increased interest in quantifying and characterizing epicardial fat which has been linked to various cardiovascular diseases such as coronary artery disease and atrial fibrillation. Recently, three-dimensional single-phase Dixon techniques have been used to depict the heart and to quantify the surrounding fat. The purpose of this study was to investigate the merits of a new high-resolution cine 3D Dixon technique for quantification of epicardial adipose tissue and compare it to single-phase 3D Dixon in patients with cardiovascular disease.MethodsFifteen patients referred for clinical CMR examination of known or suspected heart disease were scanned on a 1.5 T scanner using single-phase Dixon and cine Dixon. Epicardial fat was segmented by three readers and intra- and inter-observer variability was calculated per slice. Cine Dixon segmentation was performed in the same cardiac phase as single-phase Dixon. Subjective image quality assessment of water and fat images were performed by three readers using a 4-point Likert scale (1 = severe; 2 = significant; 3 = mild; 4 = no blurring of cardiac structures).ResultsIntra-observer variability was excellent for cine Dixon images (ICC = 0.96), and higher than single-phase Dixon (ICC = 0.92). Inter-observer variability was good for cine Dixon (ICC = 0.76) and moderate for single-phase Dixon (ICC = 0.63). The intra-observer measurement error (mean ± standard deviation) per slice for cine was − 0.02 ± 0.51 ml (− 0.08 ± 0.4%), and for single-phase 0.39 ± 0.72 ml (0.18 ± 0.41%). Inter-observer measurement error for cine was 0.46 ± 0.98 ml (0.11 ± 0.46%) and for single-phase 0.42 ± 1.53 ml (0.17 ± 0.47%). Visual scoring of the water image yielded median of 2 (interquartile range = [Q3-Q1] 2–2) for cine and median of 3 (interquartile range = 3–2) for single-phase (P < 0.05) while no significant difference was found for the fat images, both techniques yielding a median of 3 and interquartile range of 3–2.ConclusionCine Dixon can be used to quantify epicardial fat with lower intra- and inter-observer variability compared to standard single-phase Dixon. The time-resolved information provided by the cine acquisition appears to support the delineation of the epicardial adipose tissue depot.

Stephen L. Zegura (2 July 1943–26 May 2019)

Stephen L. Zegura (2 July 1943–26 May 2019) Rebecca Rogers Ackermann1,2, Michelle Bezanson3, Michael Hammer4, and David Raichlen5 Keywords Stephen l, Zegura, Obituary, Anthropology Stephen L. Zegura passed away on 26 May 2019 at the age of 75. Born in San Francisco, California, Zegura was the eldest child of Dragomir Božo Zegura and Adele (June) Perelli-Minetti. He earned his BA in anthropology, magna cum laude and with departmental honors, at Stanford University. Even as an undergraduate at Stanford, Zegura was extremely active, brainstorming creative ways to create an academic career focusing on the study of humans. His energetic appreciation for Stanford and the inspirational professors he met there was often shared with his students—he was a devoted Cardinal. He then moved to the University of Wisconsin–Madison, where he was a Woodrow Wilson Fellow, and received his master's degree and doctorate in human biology in 1971. His PhD research focused on multivariate analyses of variation in native Alaskan ("Eskimo") crania. Zegura relocated briefly to New York University before moving to the University of Arizona (U of A) in Tucson, where he stayed for the remainder of his career and life. For nearly 40 years Zegura taught biological anthropology, human evolution, and human genetics at U of A. He was the recipient of the 2009–2010 Raymond H. Thompson Award in honor of his distinguished service and contributions he made to the School of Anthropology throughout his career. How do you measure the impact of a life, especially for someone as alive—as large as life—as Steve Zegura was? He was brilliant and tough and kind and generous. He was mischievous, with a slightly irreverent sense of humor. He was an extraordinary teacher, with a sharp intellect and a passion for sharing knowledge. And Zegura was an exceptional scholar, presenting theoretically rigorous and well-written contributions, with approximately 50 journal articles to his name. He leaves behind important contributions to knowledge in these research outputs, and here, we reflect on the arc of these outputs and their relevance then and now. Zegura's first works focused on measuring skulls and applying statistical methods to differentiate them from one another and from other groups (Zegura 1971), a popular pastime in biological/physical anthropology since the discipline developed in the 1800s, and one that has deep links to racial science (Gould 1981; Sussman 2014) . Even at this early stage, Zegura displayed two traits that continued to shine throughout his research career: meticulous attention to detail and a creative ability to synthesize disparate methodologies into a coherent framework for hypothesis testing. While many skeletal biologists were continuing to use older, traditional methods to examine skeletal variation in human populations, Zegura was quick to include linguistic analyses in his studies, Click for larger view View full resolution Figure 1. Stephen Zegura, early 1970s. Photo courtesy of Elizabeth Chesney Zegura. [End Page 49] Click for larger view View full resolution Figure 2. Stephen Zegura (right) and Fred Hulse at the Arizona State Museum. Photo courtesy of Elizabeth Chesney Zegura. Click for larger view View full resolution Figure 3. Stephen Zegura's lasting impact as a scholar, teacher, and mentor: citation numbers at time of writing (23 September 2019). examining degrees of correlation between these distinct data sets (Zegura 1975). This early work on Inuit populations led to numerous highly regarded publications. By integrating linguistics and skeletal biology, Zegura was ahead of the curve, and today this work is considered highly creative and synthetic. Zegura was also an early contributor to our understanding of inter- and intraobserver measurement error in craniometric studies and the importance of conducting baseline measurement error analyses in order to accurately interpret the biological significance of any results (Utermohle and Zegura 1982; Utermohle et al. 1983), a topic that still garners considerable attention (e.g., Robinson and Terhune 2017). Ultimately, Zegura's interests turned to broader questions that highlighted the degree to which racial typology and theoretical approaches had limited the research focus of the study of prehistory in the North American Arctic (Schindler et al. 1985). In this, he was in keeping with the general movement away from typological "racial" thinking...

Understanding how axial loads on the spine influence segmental biomechanics for idiopathic scoliosis patients: A magnetic resonance imaging study

BackgroundSegmental biomechanics of the scoliotic spine are important since the overall spinal deformity is comprised of the cumulative coronal and axial rotations of individual joints. This study investigates the coronal plane segmental biomechanics for adolescent idiopathic scoliosis patients in response to physiologically relevant axial compression. MethodsIndividual spinal joint compliance in the coronal plane was measured for a series of 15 idiopathic scoliosis patients using axially loaded magnetic resonance imaging. Each patient was first imaged in the supine position with no axial load, and then again following application of an axial compressive load. Coronal plane disc wedge angles in the unloaded and loaded configurations were measured. Joint moments exerted by the axial compressive load were used to derive estimates of individual joint compliance. FindingsThe mean standing major Cobb angle for this patient series was 46°. Mean intra-observer measurement error for endplate inclination was 1.6°. Following loading, initially highly wedged discs demonstrated a smaller change in wedge angle, than less wedged discs for certain spinal levels (+2,+1,−2 relative to the apex, (p<0.05)). Highly wedged discs were observed near the apex of the curve, which corresponded to lower joint compliance in the apical region. InterpretationWhile individual patients exhibit substantial variability in disc wedge angles and joint compliance, overall there is a pattern of increased disc wedging near the curve apex, and reduced joint compliance in this region. Approaches such as this can provide valuable biomechanical data on in vivo spinal biomechanics of the scoliotic spine, for analysis of deformity progression and surgical planning.

Sex Determination of Human Crania Using 3D Surface Scanning of the Mastoid Process

Historically, sex determination of human skulls has been dependent on visual examination and qualitative scoring of sexually dimorphic features such as the mastoid process. The accuracy of this method relies heavily on observer experience. We report a new method for sex determination based on quantitative analysis of the mastoid process. A Polhemus FastScan 3D laser scanner is employed to capture cranial surface morphology. The scan protocol generates 2 mesh models that are imported and aligned using Geomagic Design X64 software to create a single digital model per cranium. From the model, the mastoid process is isolated and its volume measured. Total cranial volume is also estimated from the model, allowing computation of a mastoid ratio (mastoid volume:cranial volume) for each specimen. A pilot study was performed utilizing a small sample of crania from known-sex Medieval Nubian individuals. Results demonstrate little overlap in the range of male vs female absolute mastoid volume. Intra-observer measurement error is low. A t-test shows significant differences (p < 0.05) between male and female mastoid ratios, demonstrating the utility of this method for sex determination. Moreover, the new method is advantageous because the scan protocol is quick; it captures a permanent record of each specimen; and unlike qualitative scoring, it can be executed consistently with minimal training. Future work will focus on evaluating inter-observer error, testing the method across population samples, and devising protocols for other dimorphic features, with the goal of developing a comprehensive multivariate method for sexing skulls based on 3D surface scanning.

Observer Variability in Sonographic Measurement of Kidney Sizes among Children in Benin-City, Nigeria.

To assess the level of inconsistency in replicating sonographic kidney size measurements in a population of healthy Nigerian children. In this prospective cross-sectional study, convenience sampling technique was used to select a sample of Nigerian children. Both consent from participants and ethical approval from the local authority were obtained before the study commenced. Three radiologists carried out the replicate sonographic measurements using a DP-1100 mechanical sector scanner with a 3.5 MHz convex probe. All examinations were done with subjects in the supine oblique position. Longitudinal and transverse scans were performed. Renal lengths and widths were measured from the longitudinal scans while thickness was measured from the transverse scans. Renal volumes were calculated with the ellipsoid formula. Analysis of variance, Student's t-test, Pearson's correlation coefficient and z-test were used to test the statistical significance of results. SPSS version 17.0 was used in the analysis of results while statistical significance of all results was tested at p < 0.05. Mean intra-observer measurement errors in replicate sonographic measurements of kidney sizes ranged from 0.36-0.43 cm, 0.22-0.63 cm, 0.37-0.52 cm and 5.93-9.62 ml for kidney length, width, thickness and volume, respectively. Mean inter-observer measurement errors were in the range of 0.29-0.48 cm, 0.18-0.23 cm, 0.34-1.82 cm and 5.92-7.28 ml for length, width, thickness and volume, respectively. Mean intra-observer errors were not statistically significant (p < 0.05) but mean inter-observer errors were (p < 0.05). Differences in all measurement errors of right and left kidney length, width, thickness and volume were not statistically significant (p > 0.05). Measurement errors correlated weakly with kidney sizes. Observer errors in renal length were not significantly different from what was reported among Caucasians (p > 0.05) whereas that of volume was (p < 0.05). Errors in replicate sonographic kidney size measurements obtained by a single observer were less than errors in the same measurements by different observers; therefore, replicate sonographic measurements by a single observer were more consistent in this population.

Intra-observer error of mouse long bone cross section digitization

Digitization of periosteal and endosteal contours of bone cross section is one of several methods used for calculating long bone cross-sectional geometry (CSG). In this study, invasively obtained bone histological samples were used to calculate intra-observer measurement error for CSG parameters. Intra-observer error was measured based upon repeated measurements of cross-sectional areas (total area [TA], cortical area [CA]) and moments of area (Imax, Imin, Imax/Imin, J) in B6CBA mice (n = 17). Cross sections were cut at 50 % of the biomechanical length of the left tibia and the samples were further processed for CSG and histological analysis. Intra-observer error was measured to estimate the accuracy of the digitization method. Accuracy of the tested digitization method was expressed by mean difference (MD), mean absolute difference (MAD), and limits of agreement (LA). The results confirm our assumption that intra-observer error decreases with the number of repeated measurement events. Thus, the error can be minimized by acquiring experience in the section digitizing. Our results also show that TA, CA and polar moment of area (J) are more susceptible to intra-observer error than are Imax, Imin and Imax/Imin.

Variation in the Measurement of Cranial Volume and Surface Area Using 3D Laser Scanning Technology

Three-dimensional (3D) laser scanner models of human crania can be used for forensic facial reconstruction, and for obtaining craniometric data useful for estimating age, sex, and population affinity of unidentified human remains. However, the use of computer-generated measurements in a casework setting requires the measurement precision to be known. Here, we assess the repeatability and precision of cranial volume and surface area measurements using 3D laser scanner models created by different operators using different protocols for collecting and processing data. We report intraobserver measurement errors of 0.2% and interobserver errors of 2% of the total area and volume values, suggesting that observer-related errors do not pose major obstacles for sharing, combining, or comparing such measurements. Nevertheless, as no standardized procedure exists for area or volume measurements from 3D models, it is imperative to report the scanning and postscanning protocols employed when such measurements are conducted in a forensic setting.

Obstetric ultrasound scanning by local health workers in a refugee camp on the Thai–Burmese border

ObjectivesUltrasound examination of the fetus is a powerful tool for assessing gestational age and detecting obstetric problems but is rarely available in developing countries. The aim of this study was to assess the intraobserver and interobserver agreement of fetal biometry by locally trained health workers in a refugee camp on the Thai–Burmese border.MethodsOne expatriate doctor and four local health workers participated in the study, which included examinations performed on every fifth pregnant woman with a singleton pregnancy between 16 and 40 weeks' gestation, and who had undergone an early dating ultrasound scan, attending the antenatal clinic in Maela refugee camp. At each examination, two examiners independently measured biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL), with one of the examiners obtaining duplicate measurements of each parameter. Intraobserver measurement error was assessed using the intraclass correlation coefficient (ICC) and interobserver error was assessed by the Bland and Altman 95% limits of agreement method.ResultsA total of 4188 ultrasound measurements (12 per woman) were obtained in 349 pregnancies at a median gestational age of 27 (range, 16–40) weeks in 2008. The ICC for BPD, HC, AC and FL was greater than 0.99 for all four trainees and the doctor (range, 0.996–0.998). For gestational ages between 18 and 24 weeks, interobserver 95% limits of agreement corresponding to differences in estimated gestational age of less than ± 1 week were calculated for BPD, HC, AC and FL. Measurements by local health workers showed high levels of agreement with those of the expatriate doctor.ConclusionsLocally trained health workers working in a well organized unit with ongoing quality control can obtain accurate fetal biometry measurements for gestational age estimation. This experience suggests that training of local health workers in developing countries is possible and could allow effective use of obstetric ultrasound imaging. Copyright © 2009 ISUOG. Published by John Wiley & Sons, Ltd.

Changes in temporomandibular joint sagittal disc position over time in adolescents: A longitudinal retrospective study

Temporomandibular joint (TMJ) disc displacement (DD) is a common finding in preorthodontic adolescents. The natural progression of this disorder has not been described with magnetic resonance imaging. The TMJs of a longitudinal sample of 94 preorthodontic adolescents were evaluated with magnetic resonance imaging to quantify sagittal disc position (SDP). The average time between imaging visits (V1 and V2) was 3.7 years (range, 1-6 years). Boys and girls had significantly different SDP values at V1, and therefore changes in SDP from V1 to V2 were analyzed separately for each sex. The highest standard deviation was 0.58 mm for intraobserver measurement error. Regression analysis identified no significant association between change in disc status and time between imaging. There was no significant difference in mean change in SDP in girls or the right TMJ in boys. The boys' left TMJ showed a significant mean increase (0.87 mm of anterior displacement). Approximately 10% of right TMJs and 15% of left TMJs had more than 2 mm of anterior DD during the study. In the girls, approximately 8% of the right TMJs and 3% of the left TMJs showed more than 2 mm of posterior disc position changes from V1 to V2. A natural progression in severity of DD in adolescents was not identified. Some subjects had large increases in anterior DD.

Measurement error for ultrasound fetal biometry performed by paramedics in rural Bangladesh

To document the accuracy and precision of sonographic fetal biometry performed by nine paramedics from rural Bangladesh. Paramedics underwent intensive training (6 weeks) including hands-on practice then underwent a series of standardization exercises. Measurements of each fetus were taken by a highly-trained medical doctor (study supervisor) and the nine paramedics. Crown-rump length (CRL) in fetuses of less than 10 weeks' gestation, and biparietal diameter (BPD), occipitofrontal diameter, head and abdominal circumference (AC) and femur diaphysis length (FL) were measured twice using standard procedures by each paramedic and the medical doctor for each fetus, with at least 20 min between them. Precision was quantified using variance components analysis; the intraobserver error for each of the paramedics was calculated by comparing repeat measurements taken on the same participant, and the measurements obtained by each individual paramedic were also compared with those taken by the others (interobserver error). Accuracy was estimated by comparing the mean of the two measures taken by each paramedic to those taken by the study supervisor using paired t-tests. Bland-Altman plots were used to visually assess the relationship between precision of repeat measurements (intraobserver error) and fetal size. A total of 180 women, at 7 to 31 weeks' gestation, participated in the study. Intraobserver error of the measurements obtained by the paramedics, expressed as the mean SD, ranged from 0.97 mm for BPD in the first trimester to 7.25 mm for AC in the third trimester, and was larger than the interobserver error (i.e. accounting for a greater proportion of total variance) for most measurements. Interobserver error ranged from 0.00 mm for FL to 3.36 mm for AC, both in the third trimester. For all measurements except CRL, intraobserver error increased with increasing fetal size. The measurements obtained by the paramedics did show some statistically significant differences from those obtained by the study supervisor, but these were relatively small in magnitude. Both inter- and intraobserver measurement errors were within the range reported in the literature for studies conducted by technical staff and medical doctors. With intense training, paramedics with no prior exposure to ultrasonography can provide accurate and precise measures of fetal biometry.

A New Method of 3-D Cephalometry Part I

The purpose of this study was to present a new innovative three-dimensional (3-D) cephalometric method. Part I deals with the set-up and validation of a voxel-based semi-automatic 3-D cephalometric reference system. The CT data (DICOM 3.0 files) of 20 control patients with normal skeletal relationships were used for this study. To investigate accuracy and reliability of the 3-D cephalometric reference system (Maxilimtrade mark, version 1.3.0) a total of 42 (14 horizontal, 14 vertical and 14 transversal) orthogonal measurements were performed on each patient twice by each of two investigators. The intra-observer measurement error was less then 0.88 mm, 0.76 mm and 0.84 mm for horizontal, vertical and transversal orthogonal measurements, respectively. The inter-observer measurement error was less as 0.78 mm, 0.86 mm and 1.26 mm for horizontal, vertical and transversal orthogonal measurements, respectively. Squared correlation coefficients showed a high intra-observer and inter-observer reliability. The presented 3-D cephalometric reference system proved to be accurate and reliable and can therefore be used for 3-D cephalometric hard and soft tissue analysis.

Efficacy of three conditions of radiographic interpretation for assessment root canal length

To compare the efficacy of three conditions of image interpretation for radiographic root measurements and calculating the intra-observer reproducibility of the measurements. Thirty intra-operative periapical radiographs of maxillary central and lateral incisors were measured, in mm, from the tip of the file to the radiographic apex, using a caliper. Three separate measurements were made of the 30 radiographs. The three measurements for each tooth were averaged and the mean used for further calculations. After a 12-day period, the measurements were repeated. The three experimental viewing conditions used: 1) standard viewbox without masking of background light around the radiograph and without magnification (Visual); 2) standard viewbox with use of a magnifying lens of 2.5x and with background light masked (Magnification); and 3) viewer device that restricts room lighting and enlarges the image by a magnifying lens of 1.75x (Viewer). The mean and standard deviation of the measurements were calculated and used for descriptive analysis. Two-way analysis of variance (ANOVA) was used to evaluate intra-observer and inter-method agreement of the measurements. The measurement error was estimated by Dalhberg's formula. The ANOVA showed no significant differences between measurement sessions, viewing methods, or interaction between observation session and method (p>0.05). The intra-observer measurement error was 0.02 mm for Visual and the Magnification methods and 0.01 mm for the Viewer. There does not seem to be any advantage in using viewbox masking or magnification for measuring the distance between the end of the endodontic file and the root apex in maxillary incisors.

Measurement of gastric emptying by standardized real-time ultrasonography in healthy subjects and diabetic patients.

The aim of this study was to simplify and standardize a reproducible, well-tolerated and clinically applicable method for the assessment of gastric emptying rate by real-time ultrasonography. A total of 33 subjects were examined, including 19 healthy subjects and 14 patients with insulin-dependent diabetes mellitus and clinically suspected delayed gastric emptying. Measurements of the gastric antrum were taken in the supine position and in relation to internal landmarks to obtain a standardized cross-sectional image producing the area of a selected slice of the antrum. Diabetic patients were examined on the condition that the fasting blood glucose level was 3.5 to 9.0 mmol/l. Gastric emptying rate was estimated and expressed as the percentage reduction in antral cross-sectional area from 15 to 90 min after the ingestion of a standardized semisolid breakfast meal (300 g rice pudding, 330 kcal). Interobserver and intraobserver measurement errors were assessed, as was the significance of age and sex on gastric emptying. In comparison to healthy subjects, diabetic patients showed significantly wider median values of the 90 min postprandial antral area, but only a mild tendency toward greater dilation of the gastric antrum prior to and 15 min after meal ingestion. The median value of gastric emptying rate in these diabetic patients was estimated at 29%, which was less than half of that in the healthy subjects (63%). Statistically the difference was highly significant. Interpersonal variability of gastric emptying rate and antral areas was large for both groups. Measurements of gastric emptying rate gave highly reproducible results on separate days and from different observers (interobserver systematic measurement error 0.3% and random measurement error 10.9%; intraobserver systematic measurement error 3.6% and random measurement error 9.5%). No difference in gastric emptying rate was found related to age or sex. We conclude that the use of standardized real-time ultrasonography to determine gastric antral cross-sectional area in a single section of the stomach is a valid method for estimating gastric emptying rate.

An independent evaluation of the age-related eye disease study (AREDS) cataract grading system

PURPOSE. To assess intra- and interobserver reproducibility of the Age-Related Eye Disease Study (AREDS) system for grading lens opacities and to provide data on its capacity to reliably detect changes in lens status. METHODS. Independent and replicate grading of 40 sets of lens photographs (one slit-lamp and two retroillumination photographs) were performed by three experienced observers. Patients were participants in the Collaborative Italian-American Clinical Trial of Nutritional Supplements which is testing the effect of a mineral-multivitamin supplement on age-related cataract (CTNS). Scatterplots and intraclass correlation were used to assess measurement error. RESULTS. Analysis revealed good intra- and interobserver reproducibility of the system. Greatest intraobserver measurement error showed 100% of pairs within 10% areal difference for cortical cataract, 97.5% within 15% areal difference for posterior subcapsular cataract, and 100% within 1 density unit difference for nuclear opacity. Greatest interobserver measurement error showed 95% of pairs within 10% areal difference for cortical cataract, 97.5% within 15% areal difference for posterior subcapsular cataract, and 97.5% within 1.5 density unit difference for nuclear opacity. CONCLUSIONS. The AREDS lens opacities grading system appears to be sufficiently reliable to detect changes of at least 10% areal involvement for cortical, 15% areal involvement for posterior subcapsular, and 1.0 units for nuclear opacities. It therefore seems sufficiently sensitive to adequately monitor progression of lens opacities in a longitudinal study of patients with early cataract. Its applicability in a population with advanced or complex mixed opacities must await further testing.

Brief communication: measurement size, precision, and reliability in craniofacial anthropometry: bigger is better.

In this paper we examine the results of an intraobserver measurement error study involving 49 craniofacial variables that ranged in size from less than 1 cm to approximately 20 cm. Repeat measurements were taken on 10 male and 10 female adult subjects (19-59 years old). Our focus is on the relationship between measurement size and measurement error across the 49 variables. We found that the size of the variable showed no relationship with the magnitude of the error as measured by the technical error of measurement. When the error was expressed as a coefficient of relative variation (Malina et al.: Vital and Health Statistics, Series 11, No. 23. Washington, DC: US Department of Health and Human Services, 1973), this quantity was negatively associated with the size of the measurement. Conversely, reliability (Fleiss: The Design and Analysis of Experiments. New York: John Wiley & Sons, 1986) was positively correlated with measurement size. We did not find effects of scale (Marks et al.: Am. J. Epidemiol. 130:578-587, 1989) within the individual measurements. Thus, for the range of size of the craniofacial measurements in this study, measurement size must be added to the list of factors such as ease of locating landmarks, measurement technique, and systematic bias in the application of the technique that can affect precision and reliability in anthropometry.

Real time ultrasonography of the gastric antrum.

This study aimed to evaluate whether serial ultrasound measurements of antral volumes are reproducible and, if so, whether they are representative of the entire gastric contents and reliably measure gastric emptying. The antral volume was measured in man after oral and intragastric administration of known amounts of 5% glucose solutions, and on two separate occasions in the same subjects, after the ingestion of a standardised solid-liquid meal (1050 kcal). Antral volume measurements were performed in both supine and upright positions; inter- and intraobserver measurement errors were also assessed. After ingestion or intragastric administration of equal amounts of liquid, antral volumes determined by ultrasound showed a wide intersubject variability. In each individual subject, however, a linear trend was found between the antral volume and amount of ingested or administered liquid. Intrasubject variability of antral volume measurements was at its minimum in fasting conditions and 300 minutes after ingestion of the solid-liquid meal. Intra- and interobserver variations and whether the patient was erect or supine did not affect measurements of antral volumes. These results support the use of real time ultrasound in determining the gastric emptying time. Results at fasting and 300 minutes after a solid-liquid meal are stable end points of measurement.

MEASUREMENT ERROR IN ASSESSMENT OF VERTEBRAL ROTATION USING THE PERDRIOLLE TORSIONMETER

The Perdriolle torsionmeter assesses vertebral rotation on a spinal radiograph. It is frequently used ot measure improvement in spinal derotation following Cotrel-Dubousset instrumentation for scoliosis. In this study, Intraobserver and intraobserver measurement error was examined during use of the

Meaning of biodistance statistics: a test case using adult monozygotic twins.

Anthropometry, historically one of the primary research techniques in physical anthropology, has been widely utilized in biodistance studies. The complex genetic and environmental interaction that governs the expression of anthropometric dimensions, together with concerns over measurement error, have sometimes clouded the interpretation of biodistances based upon anthropometry. In this study, 51 pairs of adult monozygotic twins were analysed using discriminant analysis and Mahalanobis' generalized distance. Both male and female twins, grouped by first- versus second-born, displayed very small, statistically insignificant distances between groups. When literature estimates of intra-observer measurement errors were used as a frame of reference, the average absolute differences between the twin pairs were approximately twice the size of the measurement error estimates. The results of this study suggest that, first, the environmental effect upon the genetically influenced traits measured by anthropometry is not large enough to bring about significant multivariate differences between identical twin pairs; and, second, biodistance studies based upon anthropometry can be reliable so long as measurement error is minimized.