Standards from birth to maturity for height, weight, height velocity, and weight velocity: British children, 1965. II.

Standards: Chronological Age-based and Individual Type We now consider how to construct velocity standards, to answer our second question 'Has this child's rate of growth been within normal limits ?' We are again confronted with the alternatives of plotting against chronological or developmental age at adolescence and we have adopted the same solution as before. First we give, in the conven- tional manner, centiles plotted against chrono- logical age, over the whole age span. These are calculated simply from two measurements a year apart, without using further longitudinal data. They depend on a two-occasion longitudinal study, nothing further. At adolescence these standards are greatly scattered by the phase-difference effect. If we know nothing about a boy except that he is 12 years old and grew 3 cm. during the last year, we must plot 3 cm. at 11 * 5 years and interpret this according to the chronological age centiles. If, however, we know that he is mid- pubescent, or that his skeletal age is 14 * 0 years, then in theory we could make a more effective interpretation if we had the appropriate standards.