Developmental Continuity and Stability

Continuity and Stability

Continuity is consistency in the group average level of a characteristic through time (Figure 1) and conventionally indexed by similarity in the group average between times. The extant life span development literature supports short-term and long-term continuity of many biological and psychological characteristics. For example, human bodies work constantly and throughout development to maintain homeostasis, the organism’s internal consistency. Thus, the average temperature of human bodies should keep a constant 36.5°C and regulation of pH of the blood (a measure of alkalinity and acidity) a constant 7.365. Stability is consistency in the relative order, standing, or rank of individuals in a group on a characteristic through time (Figure 2) and is conventionally indexed by correlation. A stable characteristic is one that some individuals display at high levels relative to others in a group at one point in time and again display at relatively high levels at a later point in time. Personality and many aspects of context are relatively stable over time. Measuring continuity and stability demands longitudinal within-subject social and behavioral science designs.

Figure 1 Group mean and individual order consistency

Figure 2 Correlations between continuity and stability

Why Is Developmental Consistency Important?

Consistency in development is significant for several reasons. First, consistency is basic to survival and the normal function of living organisms and organizations. Diverse organismic systems strive to maintain a state of dynamic and adaptive equilibrium, and consistency—physical, chemical, biological, psychological, and environmental—is often a sign of robustness and health. Many interior forces conserve homeostasis in the individual and allostasis (the process of achieving stability through physiological or behavioral change) across development, and consistent social networks in which much of development normally transpires likewise contribute to constancy. It has been asserted that consistency is a basic psychological need, and that lovers, markets, and nation-states abhor inconstancy.

Second, consistency provides key information about development. Developmental science is concerned with description, explanation, and prediction. Continuity and stability describe the developmental courses of a characteristic, insofar as the group maintains its average level and individuals maintain their order relative to one another in their cohort. It is often observed that a major [Page 570]predictor of a characteristic at a given age is the expression of that characteristic at an earlier age (which is only true, of course, for consistent characteristics). Personality is believed to be meaningful because it is considered consistent and consequently prognostic. Consistency therefore provides insights to a practical understanding of individuals when younger and older.

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