The amount of growth achieved by a child obviously depends on the time for which growth proceeds and at the speed of growth per unit time. Measurements taken on a single individual at intervals can be plotted against time to produce a graph of progress whether they are derived from the whole body or from one of its component parts. A graph of this sort is called a “distance curve”, since any point on it indicates the distance travelled along the road to maturity. In figure 3.1 is shown the distance growth curve for height, of De MontbeiIlard’s son measured every six months from birth to eighteen years. Scamrnon produced a curve by plotting height attained” at successive ages and joining together the data points at each age, which described the height achieved at any age. Thus, the curve was known as height-for-age curve or height distance curve. The term distance is often used because it is the reflection of how far the child has progressed towards adulthood.
However, the curve is interesting for the following reasons:
- When growth is measured at intervals of regular 6 months, it gives a relatively smooth and continuous curve, not characterised by periods of no growth and then dramatic increase in stature.
- Growth is not a linear process that has an equal amount of increase in height each year.
- The curve of growth has four distinct phases, corresponding to relatively rapid growth in infancy, steady growth in childhood, rapid growthin adolescence and a very slow growth as individual approaches adulthood.
- It represents the most dramatic increase in size, for instance, 60 cm at birth to over 180 cm at adulthood. The majority of growth is however witnessed during infancy and childhood but perhaps the important physical changes occur during adolescence
- We usually cease growing in height or reach our adult height in our late teenage years, say 18 or 19 years of age. The curve demonstrated was plotted based on data collected every 6 months to obtain the half yearly patterns of growth using longitudinal method.
It is clear that pattern of growth, plotted with age against height resulting from 6 monthly measurements, is composed of different curves. During infancy, from birth to 5 years of age, it depicts a smooth curve with decaying polynomial as it gradually departs negatively from straight line with increase in time. During childhood. between 5 years and 10 years, pattern does not depart dramatically from a straight line. The pattern changes during adolescence, from 10 years to 18 years, into an S-shaped or Sigmoid curve. Cross-sectional surveys are more frequently used while undertaking studies on larger samples. Such studies also’ provide useful informatjon through distance curve of growth about status of any dimension of the body at any point of time and are helpful in constructing growth standards.