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Home›Probability and statistics

Reading charts

Korea recorded 438,400 births in 2015 and 230,000 in 2023. Draw the same eleven numbers as bars, as a line or as a pie, cut the axis and change the class width of a histogram, and see what each choice does to the picture.

Progress

Before you start

No statistics course is needed first. Reading charts here means working out differences, ratios and percent change, and telling percent from percentage points, so Decimals and percent is the most useful preparation. The examples use real counts such as Korean births and the 2020 US census.

When you finish

Afterwards you can check a chart's title, units and axes before its shape, and read 230.0 on an axis in thousands as 230,000 births. You can draw a pie slice as 38.1% of 360°, read slope on a line graph as speed of change, spot an axis that starts at 220 thousand to exaggerate a rise, and see how class width reshapes a histogram.

  1. 1How to read a chartIn the 2023 bar of a chart of Korean births, 230.0 means 230,000 babies, because the axis is labelled in thousands.
  2. 2Bar chartsThe 2020 US census counted 126,266,107 people in the South and 57,609,148 in the Northeast, so the South bar should be about 2.19 times as long.
  3. 3Pie charts and percentagesThe South held 38.1% of the US population in 2020, so its slice of a pie chart spans 38.1% of 360°, about 137°.
  4. 4Line graphs and change over timeKorea's total fertility rate fell every year from 1.24 in 2015 to 0.72 in 2023, then rose to 0.75 in 2024 and 0.80 in 2025.
  5. 5Misleading axesBirths rose 10.6% from 2023 to 2025, but on a bar chart whose axis starts at 220 thousand the 2025 bar is drawn 3.43 times as tall.
  6. 6Histograms and class widthWith classes 2 inches wide, 40 of OpenStax's 100 soccer players fall between 65.95 and 67.95 inches; shift the start to 59 and the tallest class moves.
Sources for this course (9)
  • OpenStax, Introductory Statistics 2e by Barbara Illowsky and Susan Dean (, per the page notice on 2026-10-17): 2.2 histograms, frequency polygons and time series graphs, including the 100 soccer player heights, the books bought by 50 students, class width, convenient starting points, the square root guideline, relative frequency f/n (3 of 40 = 0.075) and the section "How NOT to Lie with Statistics" (Darrell Huff, pie charts, varying class widths, axes that do not start at zero) (openstax.org/books/introductory-statistics-2e/pages/2-2-histograms-frequency-polygons-and-time-series-graphs)
  • Korean births and total fertility rate 2015 to 2025: Ministry of Data and Statistics (국가데이터처, formerly Statistics Korea)
  • "2025년 출생 통계" press release, Table 1 (mods.go.kr/board.es?mid=a10301010000&bid=204&list_no=446625, figures for calendar years 2015 to 2025)
  • TFR definition, 1970 value 4.53, 1983 value 2.06 and replacement level 2.10: e-나라지표 합계출산율 (index.go.kr/unify/idx-info.do?idxCd=5061)
  • US resident population 1950 to 2020 and the four regions in 2010 and 2020: US Census Bureau, Historical Population Change Data (1910-2020)
  • released April 26, 2021, counts as of April 1 of each census year (census.gov/data/tables/time-series/dec/popchange-data-text.html) and 2020 Census Apportionment Results press release (census.gov/newsroom/press-releases/2021/2020-census-apportionment-results.html)
  • William Playfair, Commercial and Political Atlas (1786) and Statistical Breviary (1801): Encyclopedia.com "Statistical Graphics" (encyclopedia.com/social-sciences/encyclopedias-almanacs-transcripts-and-maps/statistical-graphics)
  • J. Sachs, BRANCH (branchcollective.org)
  • I. Spence, "William Playfair and the Psychology of Graphs" (2006).

Checked: 2026-10-17