Skewness
Topic of Descriptive statistics, part of Data analysis
Skewness
| Type | Topic |
| Taught in | Descriptive statistics |
| Part | Data analysis |
| Questions using it | 4 |
A measure of asymmetry, zero for symmetric data, positive when the right tail is longer. Strongly right-skewed positive data are often summarised and modelled better after a log transformation.
In Descriptive statistics
Strongly skewed data are often easier to summarise, and to model, after a transformation. A logarithm turns ratios into differences, so it spreads out the bunched values near zero and draws in the far tail. For serum creatinine the skewness, a measure of asymmetry that is zero for symmetric data, falls from 4.4 to 1.6 on the log scale. The reciprocal, 1/x, brings it to about zero. Transformations do not change the data, only the scale they are viewed on; the order of the patients stays the same, so the median of the transformed data is the transform of the median.
Used in
- Taught in Descriptive statistics
- Also used in Confidence intervals · Estimation examples · Bayesian foundations · Introduction to generalised linear models · Paired comparisons, and how far a fit is from the data · Estimation and inference for the multivariate normal · K-means clustering
- Questions that use it (4) — Ten successive exponential components (answer) · Alcohol and school attendance (answer) · Q55 · Question 2 (answer)
- All 2 questions on Descriptive statistics
See also
Posterior point summaries · Wilcoxon rank-sum test · Sample quantile · Interquartile range · Sample variance and standard deviation · Five-number summary and boxplot · Normal quantile plot · Data table