--- title: A Tale of Two Variances: Why NumPy and Pandas Give... description: NumPy and Pandas return different variance values for the same dataset because they default to different formulas. NumPy defaults to population variance... canonical: https://daily.dev/posts/a-tale-of-two-variances-why-numpy-and-pandas-give-different-answers-7pspjqdtw twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: A Tale of Two Variances: Why NumPy and Pandas Give Different Answers | daily.dev og:description: NumPy and Pandas return different variance values for the same dataset because they default to different formulas. NumPy defaults to population variance... og:url: https://daily.dev/posts/a-tale-of-two-variances-why-numpy-and-pandas-give-different-answers-7pspjqdtw og:image: https://api.daily.dev/og/posts/7PspjqDTw.png og:image:alt: A Tale of Two Variances: Why NumPy and Pandas Give Different Answers og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # A Tale of Two Variances: Why NumPy and Pandas Give Different Answers **[Towards Data Science](https://daily.dev/sources/tds)** · 7 min read · 0 upvotes · 0 comments ## Summary NumPy and Pandas return different variance values for the same dataset because they default to different formulas. NumPy defaults to population variance (divides by N, ddof=0), while Pandas defaults to sample variance (divides by N-1, ddof=1). The difference stems from Bessel's correction, which compensates for the bias introduced when estimating population variance from a sample. The post explains the math behind both formulas, the concept of degrees of freedom, and shows how to override defaults using the ddof parameter in NumPy, Pandas, Python's statistics module, and R. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [How to use Pandas for data analysis in Python](https://daily.dev/posts/how-to-use-pandas-for-data-analysis-in-python-nxlnwvjde) · InfoWorld · 0 upvotes · 0 comments - [Polars vs pandas: What's the Difference? – Real Python](https://daily.dev/posts/polars-vs-pandas-what-s-the-difference-real-python-0uhjx2vub) · Real Python · 0 upvotes · 0 comments - [Why Random Forest Needs to Be This Random](https://daily.dev/posts/why-random-forest-needs-to-be-this-random-tqlisrjpf) · Towards Data Science · 0 upvotes · 0 comments - [What Student Performance Data Taught Me About Learning with Python](https://daily.dev/posts/what-student-performance-data-taught-me-about-learning-with-python-eclmmw7xf) · Medium · 0 upvotes · 0 comments - [Free real-world Pandas exercises, with solutions](https://daily.dev/posts/free-real-world-pandas-exercises-with-solutions-ynhgqg0gj) · Planet Python · 1 upvotes · 0 comments --- Tags: [#python](https://daily.dev/tags/python), [#data-science](https://daily.dev/tags/data-science), [#pandas](https://daily.dev/tags/pandas), [#statistics](https://daily.dev/tags/statistics), [#numpy](https://daily.dev/tags/numpy) [View this post on daily.dev](https://daily.dev/posts/a-tale-of-two-variances-why-numpy-and-pandas-give-different-answers-7pspjqdtw) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"A Tale of Two Variances: Why NumPy and Pandas Give Different Answers","url":"https://daily.dev/posts/a-tale-of-two-variances-why-numpy-and-pandas-give-different-answers-7pspjqdtw","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/a-tale-of-two-variances-why-numpy-and-pandas-give-different-answers-7pspjqdtw"},"datePublished":"2026-03-13T13:47:13.780Z","dateModified":"2026-03-13T13:47:35.967Z","description":"NumPy and Pandas return different variance values for the same dataset because they default to different formulas. 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