Mis Interpretation Of P Values
- A low P-value means the observed result is unlikely to have occurred by chance, but it does not prove causation.
- A high P-value means the observed result could have occurred by chance, but it does not prove there is no relationship.
- Interpret P-values alongside other evidence and consider alternative explanations; do not use them as the sole basis for conclusions.
Definition
Section titled “Definition”P-values are a common statistical measure used to determine the likelihood of a given result occurring by chance. Mis-interpretation of P-values occurs when people draw incorrect conclusions from those values—for example, treating a low P-value as proof of a strong relationship or causation, or treating a high P-value as proof that no relationship exists.
Explanation
Section titled “Explanation”A low P-value indicates that the observed relationship is not likely to have occurred by chance, but it does not establish that one variable causes another. Conversely, a high P-value indicates that the observed relationship could have occurred by chance, but it does not establish that there is no causal or contributing relationship. Mis-interpreting P-values in either direction can lead to incorrect conclusions because other factors, alternative explanations, or additional evidence may change the interpretation.
Examples
Section titled “Examples”Exercise and weight loss
Section titled “Exercise and weight loss”Imagine a study that examines the relationship between exercise and weight loss. The study finds that people who exercise regularly have a lower P-value for weight loss than those who do not exercise regularly. Some may interpret this to mean that exercise causes weight loss. However, a low P-value simply indicates that the relationship between exercise and weight loss is not likely to have occurred by chance. It does not prove that exercise causes weight loss.
Pollution and asthma rates
Section titled “Pollution and asthma rates”Imagine a study that examines the relationship between pollution and asthma rates. The study finds that there is a high P-value for the relationship between pollution and asthma rates. Some may interpret this to mean that pollution does not cause asthma. However, a high P-value simply indicates that the relationship between pollution and asthma rates could have occurred by chance. It does not prove that pollution does not cause asthma.
Notes or pitfalls
Section titled “Notes or pitfalls”- Mis-interpreting P-values can produce incorrect conclusions, such as assuming causation where none is proven or dismissing a contributing factor because of a non-significant P-value.
- To avoid mis-interpretation: carefully interpret study results, examine all available evidence, consider all possible explanations, and recognize that P-values are only one piece of the evidence and should not be the sole basis for conclusions.
Related terms
Section titled “Related terms”- P-value
- Causation
- Chance
- Relationship between variables