--- title: "Exploratory Analysis and an Honest Chart" description: "Before modelling anything, look: distributions, outliers, relationships between pairs. Then the chart that reports it has to make the truth easy to read, which rules out a truncated axis, a misleading" canonical: https://lightmysky.com/learn/computing/exploratory-analysis-and-an-honest-chart-mt_Jpb78Z6Ytu source: https://lightmysky.com/learn/computing/exploratory-analysis-and-an-honest-chart-mt_Jpb78Z6Ytu.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Exploratory Analysis and an Honest Chart Before modelling anything, look: distributions, outliers, relationships between pairs. Then the chart that reports it has to make the truth easy to read, which rules out a truncated axis, a misleading area, and a colour scale nobody can order. Subject: Computing · Area: Data & Databases · Ages 21 to 22 Page: https://lightmysky.com/learn/computing/exploratory-analysis-and-an-honest-chart-mt_Jpb78Z6Ytu ## Ready when they can - Choose the chart that suits a distribution, a comparison and a relationship - Redraw a chart with a truncated axis and say what changed in the reader's impression - Say what an outlier in an exploratory plot should prompt before it is removed ## Lesson: Look first, then chart it honestly Before modelling anything, you look: shapes of distributions, strange points, and how pairs move together. A long tail on one side is called skew, and it is named after the side the tail points to. A scatterplot comes before any correlation number, because numbers alone hide shape. **Example.** You plot hours of practice against quiz score, one dot per student. The cloud slopes upward with one far dot. You check that student first instead of deleting the dot. If the check proves an error, like a broken sensor, you may remove it and write down why. Match the chart to the job: a histogram or box plot for a distribution, a bar chart for a comparison, a scatterplot for how two numbers move together, and a line chart for change over time. In a relative frequency histogram each bar shows the fraction of the sample in its bin, so the bars add up to 1. A pie shows one set as fractions of a whole. Categories, like pet types, go in a bar chart, a pie or a frequency table, while a histogram bins measured numbers into ranges. Correlation needs two numbers per item, like height and weight. A truncated axis stretches small gaps into big drama, so start bars at zero. When you redraw it honestly, say what the first version made the reader believe. A frequency table lists each value with how often it happened. To find the mean, multiply each value by its frequency, add the products, and divide by the total of the frequencies, not by the number of rows. Say 3 homes have 0 pets, 2 have 1 pet, 2 have 2 pets and 1 has 4 pets. The products are 0, 2, 4 and 4, which make 10 pets across 3 + 2 + 2 + 1 = 8 homes, so the mean is 10 / 8 = 1.25 pets per home. **Recap.** Plot first, match the chart to the question, start bars at zero, and question outliers before you touch them. ## Practice 16 questions on this page, each with its working shown. ## Needs first - [Cleaning Real Data: Missing, Duplicated and Wrong](https://lightmysky.com/learn/computing/cleaning-real-data-missing-duplicated-and-wrong-mt_qIsLXA-7EC) ## Optional connections - [Straightening Data with Logarithmic Graphs](https://lightmysky.com/learn/mathematics/straightening-data-with-logarithmic-graphs-mt_TVar2jxRMI) ## Opens up - [Reading a Systems or Machine-Learning Paper](https://lightmysky.com/learn/computing/reading-a-systems-or-machine-learning-paper-mt_4LsuT0TdxT) - [Reading a Paper: the Claim, the Evidence and the Assumption](https://lightmysky.com/learn/science/reading-a-paper-the-claim-the-evidence-and-the-assumption-mt_YFgMvbohC0)