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Descriptive Statistics

Mean, median, mode, standard deviation, variance, quartiles and the interquartile range — the measures that summarize and describe a data set you already have.

13 articles

Illustration: Internal consistency: the more the items correlate, the higher the reliability

Sep 24, 20268 min read

Cronbach's Alpha: Measuring the Reliability of a Scale

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Illustration: Bar width is the weight: heavier values pull the mean toward them

Sep 23, 20267 min read

Weighted Mean and Geometric Mean: Beyond the Simple Average

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Illustration: Agreement between two raters, corrected for the agreement expected by chance alone

Sep 21, 20268 min read

Cohen's Kappa: Measuring Agreement Beyond Chance

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Illustration: A stem-and-leaf plot keeps every value while showing the shape of the distribution

Sep 17, 20267 min read

Stem-and-Leaf Plots: How to Draw, Read, and Compare Them

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Illustration: Points in the blue quadrants add to the covariance; points in the red ones subtract

Sep 15, 20268 min read

Covariance: Measuring How Two Variables Move Together

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Illustration: A histogram bins the data; the cumulative curve (ogive) reads off the median

Sep 13, 20268 min read

Frequency Distributions and Histograms: Choosing Classes and Reading the Shape

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Illustration: Points beyond the fences are flagged for investigation, not automatic deletion

Sep 11, 20267 min read

Outlier Detection: The IQR Rule, Z-Scores, and What to Do Next

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Illustration: Same mean and variance, different shape: heavier tails and flatter tops

Sep 7, 20267 min read

Skewness and Kurtosis: Measuring a Distribution's Shape

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Illustration: The level of measurement decides which statistics and tests are valid

Aug 31, 20267 min read

Types of Data: Nominal, Ordinal, Interval, and Ratio Explained

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Illustration: One extreme value inflates the standard deviation but barely moves the MAD

Aug 21, 20267 min read

Median Absolute Deviation: A Spread Measure That Ignores Outliers

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Illustration: Quartiles split ordered data into four groups of equal size

Aug 15, 20268 min read

Percentiles and Quartiles: What They Mean and How to Calculate Them

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Illustration: Relative spread lets you compare variability across different units and scales

Aug 4, 20266 min read

Coefficient of Variation: Comparing Variability Across Different Scales

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Illustration: In a right-skewed distribution the long tail drags the mean above the median

Aug 1, 20269 min read

Mean, Median, and Mode: When to Use Each One

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