Interpretation of a Correlation Coefficient of +0.8
A correlation coefficient of r = +0.8 indicates a strong positive linear relationship between birth weight and cognitive development, meaning that as birth weight increases, cognitive function commonly increases as well. 1
Understanding the Correlation Coefficient
The correlation coefficient ranges from -1 to +1, where:
- Positive values (+0.8 in this case) indicate a direct relationship where both variables move in the same direction 1
- Values closer to +1 represent stronger linear associations 1
- A coefficient of +0.8 is considered a strong positive correlation, indicating that higher birth weight is associated with better cognitive outcomes 2
Interpreting the Magnitude
- The value of +0.8 demonstrates that approximately 64% (r² = 0.64) of the variability in cognitive development can be attributed to its linear relationship with birth weight 3
- This is substantially stronger than weak correlations (r < 0.3) or moderate correlations (r = 0.3-0.7) 2
- The positive sign definitively rules out an inverse relationship, making option A incorrect 1
Clinical Context from the Evidence
While the provided evidence doesn't directly address birth weight and cognition correlation studies, related research demonstrates:
- Prenatal factors including maternal bone lead burden show inverse correlations with infant cognitive development (Mental Development Index decreased 1.6 points per 10-µg/g increase in maternal patellar lead), illustrating how prenatal exposures affect neurodevelopment 4
- Human milk components show positive correlations with infant cognitive outcomes, with synergistic effects between nutrients like choline, lutein, and DHA on recognition memory at 6 months 4
Answer to the Question
Option C is correct: "weight birth commonly increase cognitive Development" - though grammatically imperfect, this option accurately captures that higher birth weight is commonly associated with increased cognitive development, which is precisely what r = +0.8 indicates 1, 2
Option B ("little increase") would be incorrect as it understates the strength of the relationship - a correlation of +0.8 represents a strong, not small, association 2
Important Caveats
- Correlation does not equal causation - while r = +0.8 shows strong association, it doesn't prove birth weight directly causes improved cognition 3
- The correlation assumes a linear relationship between the variables, which should be verified with scatter plot visualization 3
- Outliers or restricted range of birth weights in the sample could distort the correlation coefficient value 5, 3