Statistics, worked through.

23 methods used to describe and question business numbers, each explained in plain words and worked on the same 30 days of sample data, with Excel, SQL and Python that return the same answer.

The data is 30 made-up days of orders from one store, including one sale day that behaves very differently from the rest. Download it as daily.csv; every page shows it in full.

Averages

Spread and outliers

Standard deviation · Excel, SQL, Python
Variance · Excel, SQL, Python
Range · Excel, SQL, Python
Interquartile range (IQR) · Excel, SQL, Python
Percentile · Excel, SQL, Python
Z-score · Excel, SQL, Python
Finding outliers with the IQR rule · Excel, SQL, Python
Coefficient of variation · Excel, SQL, Python
Mean absolute deviation · Excel, SQL, Python
Skewness · Excel, SQL, Python
Kurtosis · Excel, SQL, Python

Relationships between numbers

Correlation coefficient · Excel, SQL, Python
Linear regression (slope) · Excel, SQL, Python
R-squared · Excel, SQL, Python

Uncertainty and testing

Two-sample t-test · Excel, Python
Standard error of the mean · Excel, SQL, Python
Confidence interval for a mean · Excel, Python

Trends over time

Moving average · Excel, SQL, Python
Linear trend forecast · Excel, SQL, Python

For business formulas such as conversion rate, CAC or churn, see business metrics. New to analysis? Start with how to do data analysis, which method answers which question or six worked examples.

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