Longitudinal Method of Studying Growth — 2015 Paper I

Approach

• Demand of Question: Explain the longitudinal method used in human growth studies and evaluate its major advantages and limitations.
• Structuring the Response: Define repeated observation of the same individuals, describe its procedure and contrast its strengths with practical limitations.
• Key Dimensions to Cover: Same subjects, repeated measurements, growth velocity, individual variation, puberty, attrition, cost and mixed-longitudinal design.

Model Answer

Introduction: The longitudinal method studies human growth by repeatedly measuring the same individuals at successive ages over a specified period. It differs from the cross-sectional method, which examines different individuals at different ages at one point in time.

For example:

Child at 6 years → 7 years → 8 years → 9 years

Measurements may include:

• stature;
• weight;
• sitting height;
• skeletal maturation;
• body composition;
• sexual maturation.

Advantages

1. Reveals the actual growth trajectory of an individual.
2. Allows calculation of growth velocity.
3. Identifies timing of the adolescent growth spurt.
4. Demonstrates individual differences in:
   • tempo;
   • timing;
   • maturation.
5. Helps study relationships between early and later growth.

Limitations

• expensive and time-consuming;
• subject attrition may occur;
• repeated observation may extend for many years;
• changing measurement techniques can affect comparability;
• relatively small samples may reduce representativeness.

A mixed-longitudinal design combines overlapping age cohorts to reduce study duration.

Conclusion: Despite logistical limitations, the longitudinal method is especially valuable because it reveals the dynamic process, velocity and individual pattern of human growth, which cross-sectional studies cannot directly provide.