II. evaluation of biological maturation by means of maturity criteria.

Maturation may be conceived of as a series of gradual transformations through time going on in the human body from conception to death as part of the life cycle of the organism. Maturity should be used as the general concept of any specified stage - or level -during the process of maturation. The maturity level can be assessed by examining the attainment of various maturity criteria relating to dental development, skeletal development and pubertal development. In a group of children the attainment can be analyzed by probit analysis using a logarithmic time concept (logarithmic conceptional age). This is exemplified by the attainment of breast stages according to Tanner (10) in the girls of the present study. When examined a child will be rated as being within a certain stage of maturity. The least advanced and the most advanced maturity level consistent with the rating can be established using the probit lines. The relative maturity level is then expressed in SD-scores of the Gaussian fitted distributions of age at attainment of various maturity criteria in a reference group of children. This is a laborious approach when there are many series of maturity criteria, e.g. in the assessment of skeletal maturity. In such cases each stage is instead given a certain maturity score. The individual maturity level is calculated by averaging the maturity scores of the stages, which are then evaluated in SD-scores by comparing with the Gaussian fitted distribution of averaged maturity scores at that age. In both approaches discussed in this paper the evaluation of individual maturity is made with a relative scale of measurement. Accordingly, the rate of maturation can only be assessed indirectly.