(L9) Correlations

Correlation: definition, co-variables, and coefficient range

1. Correlation: A research investigation measuring the extent of a relationship between two variables.
2. Co-variables: The variables that are measured and compared against each other.
3. Range: Quantified by a correlation coefficient ranging from $-1.0$ (perfect negative) to $+1.0$ (perfect positive), with $0$ indicating no relationship.

Type of graph used to visually represent a correlation

Scattergram (scatter plot), which plots data points to visually display the relationship and pattern between two co-variables.

Characteristics of perfect, high, and low correlations

1. Perfect: Data points form an exact straight line ($+1.0$ or $-1.0$).
2. High / Strong: Data points cluster closely along a clear directional trend (values close to $+1.0$ or $-1.0$, such as $\pm 0.8$).
3. Low / Weak: Data points are widely spread apart with only a slight directional trend (values close to $0$, such as $\pm 0.3$).

Difference between positive and negative correlations

1. Positive Correlation: Both co-variables move in the same direction (as one variable increases, the other variable increases).
2. Negative Correlation: Co-variables move in opposite directions (as one variable increases, the other variable decreases).

Strengths of using correlations

1. Preliminary research tool: Serves as a good starting point to identify patterns and relationships before conducting further experimental studies.
2. Ethical feasibility: Allows investigation of variables that would be unethical, harmful, or impractical to manipulate experimentally.

Weaknesses of using correlations

1. Cannot establish cause and effect: Merely shows that a relationship exists, not that one variable directly causes change in the other.
2. Third-variable problem: An unmeasured intervening variable may actually be responsible for the observed relationship.