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Descriptive statistics
Mean, median, spread — and a chart
What does it mean?
With skewed data or outliers, the median describes the centre better than the mean. In your paper: M = 4.2, SD = 1.1.
Learn more
- Levels of measurementVariables are nominal, ordinal, interval or ratio. The level decides which averages, charts and statistical tests you are allowed to use.
- Descriptive statisticsDescriptive statistics summarize your data with numbers, tables and charts: sample size, central tendency (mean, median) and spread (SD, IQR).
- Mean, median, modeThe mean is the arithmetic average, the median the middle value, the mode the most frequent value. Use the median for skewed data or outliers.
- Standard deviation and varianceThe standard deviation is the typical distance of values from the mean. Variance is its square. Sample formula: SD = √(Σ(x − M)² / (n − 1)).
- Testing for normalityCheck normality with a histogram or Q-Q plot, skewness and kurtosis, and the Shapiro-Wilk test. With large samples, plots matter more than p-values.
- Confidence intervalA 95% confidence interval gives a range of plausible values for a population parameter. It shows both the size of an estimate and its precision.
