Interpretation of a Correlation Coefficient of +0.8 Between Birth Weight and Cognitive Development
A correlation coefficient of +0.8 indicates a strong positive linear relationship, meaning that as birth weight increases, cognitive development commonly increases as well—the answer is C.
Understanding the Correlation Coefficient
The correlation coefficient (r = +0.8) is a statistical measure that quantifies the strength and direction of a linear relationship between two continuous variables 1. The value ranges from -1 to +1, where:
- Positive values indicate that both variables move in the same direction 1
- Values closer to +1 represent stronger linear relationships 1
- A coefficient of +0.8 is considered a strong positive correlation 1
Clinical Context: Birth Weight and Cognitive Outcomes
The strong positive correlation observed in this research question aligns with established clinical evidence:
- Poor intrauterine growth (reflected by lower birth weight) predicts lower IQ and communication skills in children 2
- Lower birth weight associates with worse developmental test scores, with effects compounded by growth failure in infancy and toddlerhood 2
- The mechanism involves reduced cerebral oxygen delivery and consumption during fetal development, with cerebral oxygen consumption directly correlated with fetal brain volume 2
Interpreting the Specific Options
Option A (Inverse relation) is incorrect because the positive sign (+0.8) indicates variables move together, not in opposite directions 1.
Option B (slight increase) underestimates the relationship strength. A correlation of +0.8 represents a strong association, not a weak or slight one 1.
Option C (commonly increase) correctly captures that this strong positive correlation means higher birth weights are commonly associated with better cognitive development 2, 1.
Important Caveats
- Correlation does not equal causation: While r = +0.8 shows a strong association, it does not prove that birth weight directly causes cognitive development changes 1
- Linear assumption: The Pearson correlation coefficient assumes a linear relationship between variables 1
- Range sensitivity: The correlation coefficient can be affected by the range of observations in the sample 3
- Confounding factors: Multiple variables influence both birth weight and cognitive development, including maternal nutrition, prenatal care, socioeconomic status, and genetic factors 4, 2