Descriptive statistics
IB Psychology· Research methodology· 11 min read
1. Core concept
Descriptive statistics summarise a dataset in a few numbers. Measures of central tendency give a typical value: the mean (arithmetic average), the median (middle value) and the mode (most frequent). Measures of dispersion give the spread: the range (highest minus lowest), the standard deviation (average distance from the mean) and the semi-interquartile range. Which to use depends on the data — the mean and standard deviation suit symmetric interval data, while the median and range are more honest when the data are skewed or have outliers.
2. Key studies
IB Psychology answers must be supported by named studies. Learn these to cite as evidence:
Asch (1951)
About 35.7% of responses on critical trials were incorrect and 74% of participants conformed at least once. — Reports its results as descriptive summary statistics (percentages) — the kind of figures used to communicate a pattern at a glance.
3. Evaluation (AO3)
Strength — clear and communicable — A few well-chosen numbers convey the typical value and the spread of a whole dataset instantly.
Limitation — can hide the distribution — A single average conceals shape — the mean is dragged by outliers and skew — so reporting central tendency without dispersion can mislead.
4. Scope
5. Common Pitfalls
Wrong move:
The mean is always the best average.
Why:
A frequently penalised misconception in IB Psychology exams.
Correct move:
With skewed data or outliers the mean is pulled away from the typical value, so the median is more representative. Match the measure to the shape of the data, and always pair central tendency with a measure of spread.
Going deeper
- Inferential statisticsinferential tests are built on these summaries (RM_6).
- Descriptive vs inferential statisticsdescriptive vs inferential framing is RM_3.