Reliability of three length measurement techniques in term infants

To describe and compare the intra- and interexaminer reliability of three length measurement techniques and to determine if the three measurement techniques yield significantly different measurements.

Two experienced, mother-baby nurses each obtained length measurements using the supine, paper barrier, and Auto-length measurement techniques twice each from 48 healthy term infants. The nurses were blind to their own and to each other's measurements. The order of the nurses and the order of the measurement techniques were randomized.

For intraexaminer reliability, RN-1 had smaller mean absolute differences for the Auto-length measurements. RN-2 had similar mean absolute differences for all three measurement techniques. The percentage of differences < or = 1 cm were smallest for the supine measurements for RN-1 and not remarkably different between the measurement techniques for RN-2. For interexaminer reliability, the mean absolute differences between the pairs of measurements were smallest for the Auto-length measurements for Set-1 and for the paper-barrier measurements for Set-2. The percentage of differences < or = 1 cm between the pairs of measurements for Set-1 were not remarkably different and were lowest for the supine measurements for Set-2. The mean measurements obtained by the supine, paper-barrier, and the Auto-length measurements were respectively: 50.88, 50.33, and 49.67 cm. The differences between the means were statistically significant (X2 = 56.56, p = .0000).

The differences between length measurements by individual examiners and pairs of examiners are relatively large. Clinicians should be aware of the magnitude of error in length measurements and should interpret length measurements with caution. These findings also demonstrate that all clinicians in any setting should use the same technique to obtain length measurements.