A box plot shows: Min, Q1 (25th percentile), Median, Q3 (75th percentile) and Max.
IQR = Q3 − Q1. Outliers: values below Q1 − 1.5×IQR or above Q3 + 1.5×IQR.
Box plots are ideal for comparing distributions side by side.
Reach for this tool when characterising data for research, quality control, or business analysis. The results follow standard statistical definitions and are compatible with further inferential analysis.
A frequent mistake is computing statistics on a dataset without checking for data entry errors, outliers, or missing values. A single transcription error in a small dataset can shift the mean and standard deviation substantially. Always verify the input data before interpreting results.
A teacher calculates the class average and standard deviation for an exam: mean 64%, SD 18%. The high SD suggests a wide spread of performance levels — indicating the class may need differentiated support rather than a single revision strategy.
Interquartile Range = Q3 − Q1. It contains the middle 50% of the data.
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