LMS method for standarising language scores

Scores on six language indices assessing receptive and expressive functioning of children were obtained from the SCALES population survey. Participants were aged between 5 and 9 years. The LMS method of standardisation, which allows for skewed measurements, was used for the construction of language norms. We made use of probability weights that were produced from a two-step logistic model. Distributions of estimated z-scores from an intensively assessed sub-population and from the full population were contrasted to demonstrate the role of weights. Non-overlapping centile curves and standardised scores at each age were obtained. The use of weights was essential at retrieving the target distribution of the scores. An online calculator that estimates standardised scores for the language indices was constructed and made freely available.The findings highlight the usefulness and flexibility of the LMS method at dealing with the standardisation of linguistic and educational measures that are sufficiently continuous. The paper adds to the existing literature by providing population norms for a number of language tests that were calculated from the same group of individuals.