Accounting for measurement error: a critical but often overlooked process.
OBJECTIVE
Due to instrument imprecision and human inconsistencies, measurements are not free of error. Technical error of measurement (TEM) is the variability encountered between dimensions when the same specimens are measured at multiple sessions. A goal of a data collection regimen is to minimise TEM. The few studies that actually quantify TEM, regardless of discipline, report that it is substantial and can affect results and inferences. This paper reviews some statistical approaches for identifying and controlling TEM. Statistically, TEM is part of the residual ('unexplained') variance in a statistical test, so accounting for TEM, which requires repeated measurements, enhances the chances of finding a statistically significant difference if one exists.


METHODS
The aim of this paper was to review and discuss common statistical designs relating to types of error and statistical approaches to error accountability. This paper addresses issues of landmark location, validity, technical and systematic error, analysis of variance, scaled measures and correlation coefficients in order to guide the reader towards correct identification of true experimental differences.


CONCLUSIONS
Researchers commonly infer characteristics about populations from comparatively restricted study samples. Most inferences are statistical and, aside from concerns about adequate accounting for known sources of variation with the research design, an important source of variability is measurement error. Variability in locating landmarks that define variables is obvious in odontometrics, cephalometrics and anthropometry, but the same concerns about measurement accuracy and precision extend to all disciplines. With increasing accessibility to computer-assisted methods of data collection, the ease of incorporating repeated measures into statistical designs has improved. Accounting for this technical source of variation increases the chance of finding biologically true differences when they exist.
Harris
Edward F
EF
Department of Orthodontics, The Health Science Center, University of Tennessee, Memphis, TN 38163, USA. eharris@utmem.edu
Smith
Richard N
RN
D003625:Data Collection / Q000592:standards*; D006801:Humans; D015233:Models, Statistical; D015588:Observer Variation; D009811:Odontometry / Q000592:standards*; D015203:Reproducibility of Results; D012107:Research Design; D014070:Tooth / Q000033:anatomy & histology*