Reliability of transportable instruments for assessment of infant length

Transportable instruments for use in home and field settings have been used for decades on the basis of assumed reliability. This article describes a study that compares two portable devices for measuring length, the tape measure and the Measure Mat, against a clinical standard stadiometer with two convenience samples of Hispanic and African-American infants in an urban general pediatrics practice setting. Mean net difference between the stadiometer and the tape measure was 1.68 inches in the first sample and 0.92 inches in the second; the difference between the stadiometer and the Measure Mat was 0.92 inches. The least variability and random error (SD = 0.57 inch) was shown in the paired measurements using the stadiometer and the Measure Mat. Bland-Altman plots showed positive bias for both portable devices across the range of measurements.