Problems and limitations in studies on screening for language delay.

This study discusses six common methodological limitations in screening for language delay (LD) as illustrated in 11 recent studies. The limitations are (1) whether the studies define a target population, (2) whether the recruitment procedure is unbiased, (3) attrition, (4) verification bias, (5) small sample size and (6) inconsistencies in choice of "gold standard". It is suggested that failures to specify a target population, high attrition (both at screening and in succeeding validation), small sample sizes and verification bias in validations are often caused by a misguided focus on screen positives (SPs). Other limitations are results of conflicting methodological goals. We identified three such conflicts. One consists of a dilemma between unbiased recruitment and attrition, another between the comprehensiveness of the applied gold standard and sample size in validation and the third between the specificity of the gold standard and the risk of not identifying co-morbid conditions.