Psychometric equivalence of an improved Basic Language Morningness (BALM) scale using industrial population within comparisons.

An existing 13-item composite circadian rhythm 'morningness' scale was simplified into a '(BA)sic (L)anguage (M)orningness' (BALM) scale at a seventh grade (12-13 years) reading level. It was given to 150 each of continuously rotating shifworkers and fixed-schedule dayworkers in an industrial manufacturing plant. Multiple factor analyses confirmed three prior identified factors, morningness/effort, morning alert, and evening. Morningness scores for dayworkers were higher than for shiftworkers (p < 0.001). The BALM scale revision is suitable for most worker levels. A suggested psychometrically 'purer' 9-item morningness scale omits the inconsistent evening factor scale items.