Analysing four Norweigian population-based samples using the six-month version of the Ages and Stages Questionnaire showed few relevant clinical differences.

We investigated whether there were clinically relevant differences in the area mean scores of the six-month Ages and Stages Questionnaire (ASQ) between four Norwegian population-based samples.Area mean scores and standard deviations (SDs) were investigated for the five developmental areas of the ASQ: communication, gross motor, fine motor, problem solving and personal-social. Sample sizes varied from 166 to 1,192 and the ASQ was completed on paper or by computer. ASQ scores in the four samples were compared using ANOVA and Tukey's procedure was used to adjust for multiple comparisons.The ASQ mean area scores were generally similar in the four data sets, with few clinically relevant differences, defined as a mean difference of greater than five points, which is the smallest increment in area score, or an effect size of > 0.5 in absolute value. All the clinically relevant differences occurred when samples used a modified ASQ administration format. Several additional minor differences were statistically significant, which was expected due to the large samples.These results support the original Norwegian normative findings for the ASQ six-month form and the ASQ's use as a low-cost developmental screening tool in Norway, at least when the original format is administered. This article is protected by copyright. All rights reserved.