INTRODUCTION

It is well recognised that chronological age (CA) is a poor measure of maturity (Tanner, 1962). An average-maturing boy completes his growth in stature at 18 years of age whereas an early developer may do so at 15 or 16 years; the late-developer will still be growing as late as 20 years of age. With girls the same is true except that the whole process occurs some two years earlier. In a similar way, an average boy shows the first obvious signs of puberty, genitalia stage 2, at an age of 12 years. In contrast, the earliest developing boy within the normal range will do the same before his tenth birthday and a rather late-developing boy may still show no signs of puberty at the fourteenth birthday. In girls similar situations obtain: the average girl reaches breast stage 2 soon after 11 years of age but the earliest developers may show the same signs by nine years of age and the latest not before the thirteenth birthday. These variations in the progress of maturation introduce a new dimension to the process of growth and development, for which the name ‘tempo’ was coined by Boas (Tanner, 1981). Quantification of tempo requires the use of some measure of maturational progress and it is therefore helpful to explore what methods are available and compare them in terms of their value and validity.