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Month-over-month comparison

As explained in The Well-Grounded Data Analyst

Month-on-month change is the difference in a measure between one month and the preceding month.

A month-over-month comparison measures the difference between one month and the preceding month. For a product’s sales volume, compare November with December to find products that grew during a sale period. section 4.4.3

Build a useful comparison by checking the metric and its assumptions:

  • Start with absolute change, then inspect its distribution for outliers and values centered around zero. section 4.4.3
  • Use percentage change when product sizes differ, calculating 100 × change divided by the preceding month’s volume. section 4.4.3
  • Remove missing and infinite percentages, and treat division by zero as a separate case rather than an ordinary percentage increase. section 4.4.3

December sale analysis

Compare each product’s November and December volumes, examine the percentage-change histogram, and select products exceeding a 200% increase with more than 10 November sales. Handle products with no November sales using a separate December-volume threshold, then join category, subcategory, and brand information for interpretation.

How The Well-Grounded Data Analyst covers it

How deep it goes
Explains absolute and percentage calculations, distributions, outliers, missing values, infinity, and minimum-volume filters.
Examples
Uses November-to-December product volume, histograms, percentage changes, and category, subcategory, and brand rankings.
What it assumes
Assumes product-level monthly volumes and a defined preceding-month comparison, while teaching metric choice and data-quality handling.
What you can do after
Evaluate product growth by calculating, filtering, visualizing, and interpreting month-over-month changes.
How it connects
Connects product metrics with revenue, unique users, sales volume, outliers, conversion rate, and data quality.
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Related concepts

This explainer was generated by Manning's knowledge graph from the text of The Well-Grounded Data Analyst. The section links point to the parts of the book it draws on.