Exercise: Length of femur

This website is for students following the M.Sc. in Evidence Based Practice at the University of York.

The following is the abstract of a paper:

Objective: To assess the intra- and interobserver reproducibility of songograpbic measurement of fetal femur length between 10 and 16 weeks of gestation.

Methods: Femur length was measured three times by the same trained observer in each fetus of 136 pregnant women. A second trained observer then repeated the measurements. The coefficient of variation, intraclass correlation coefficient and repeatability coefficient with 95% CIs were calculated for each observer and between the two observers.

Results: The inter- and intraobserver repeatabilities of femur length were good. For interobserver correlation, the coefficient of variation was 4.6% (95% CI, 3.0-6.2), the intraclass correlation coefficient was 0.82 (95% CI, 0.69-0.95) and the repeatability coefficient was 2.1 (95% CI, 1.8-2.7). For intraobserver correlation, the coefficient of variation was 4.2% (95% CI, 3.2-5.6), the intraclass correlation coefficient was 0.91 (95% CI, 0.75-0.97) and the repeatability coefficient was 3.23 (95% CI, 2.33-3.86) for Observer 2. Similar results were obtained for the other observer.

Conclusion: Transvaginal femur length measurement is technically feasible and easy to perform between 10 and 16 weeks of gestation. The high degree of intra- and interobserver repeatability indicates it to be a reproducible method.

(Source: Rosati P, Bartolozzi F, Guariglia L. Intra- and interobserver repeatability of femur length measurement in early pregnancy. Ultrasound in Obstetrics & Gynecology 2004; 23: 599-601.)

Questions about this abstract:

1. What is the difference between intraobserver and interobserver reproducibility?
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2. What is meant by ‘the intraclass correlation coefficient was 0.82’ and what can we conclude?
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3. What are the advantages and disadvantages of the intraclass correlation coefficient in the study of the reliability of measurements?
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4. What is meant by ‘the coefficient of variation was 4.6%’? When is this method appropriate?
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5. What is meant by ‘the repeatability coefficient was 2.1’? In what units would this coefficient be measured?
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6. The intraobserver repeatability coefficient was 3.8 and the interobserver repeatability coefficient was 2.1. Why should this be very surprising?
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Last updated: 23 February, 2007.

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