Assessing skin pigmentation in epidemiological studies: the reliability of measurements under different conditions

Different devices are used for the non-invasive measurement of (constitutive) skin pigmentation in (epidemiological) studies. Reproducibility of measurements with the Chromameter (CM, model CR 300, Minolta, Osaka) and the Reflectometer (RM, Courage & Khazaka, Cologne) has not yet been examined in detail and was addressed in a set of four experiments and studies respectively.

Regarding the CM, the Y value of the Yxy CIE 1931 colour system was utilized, representing lightness in this colour space, while the RM measured reflectance at 660 nm with a small bandwidth of 20 nm. Both devices measure reflectance on a scale from 0 to 100%, however, in different wavelength ranges. Between 3 and 20 repetitions were performed on standard grey scales and different sets of human volunteers, including RM measurements in a large epidemiological field study.

While the coefficient of variation (V) increases and the intraclass correlation coefficient decreases from controlled laboratory to field conditions, reproducibility remained in a range considered acceptable, if adequate study conditions were maintained. In a direct comparison on human skin, V of the RM was significantly smaller than that of the CM.

Both devices can be used confidently in field studies; however, based on considerations of skin optics and in view of slightly lesser variability, the RM may be preferable.