Statistical charts

1Summary 重點摘要

Each chart has a strength: bars compare amounts, pies show proportions, lines show trends. Pick the right one.

2Vocabulary cards Vocabulary

3Step by step Steps

1. What statistical charts are forStatistical charts draw data as pictures so readers grasp the point at a glance instead of reading numbers one by one. Typical uses: comparing which subject is most popular, spotting which month had the most rain, showing the class's height distribution. A data table gives exact figures while a chart highlights shape and trend — the two complement each other. The charts in newspapers and news reports use these same three basic types, and once you can draw and read them, you can judge whether a chart exaggerates or misleads — an important media skill.
2. Bar charts: comparing categoriesA bar chart compares quantities across categories with bar heights — perfect for 'which is more' questions. Surveying favourite subjects: Chinese 25 people, English 20, Maths 30, drawn as three bars with Maths tallest and English lowest.
   
   
   
   Drawing points: categories on the horizontal axis, quantities on the vertical starting at 0; equal bar widths with even gaps; numbers marked at the tops. Bar charts excel at precise comparison — the difference in height is exactly the difference in quantity.
3. Pie charts: proportionsA pie chart shows each part's share of the whole with sector sizes — ideal for 'what proportion' questions. Subject preferences: Chinese 25%, English 20%, Maths 30%, Others 25%, and all parts must sum to exactly 100%.
   
   
   
   Each sector's angle = percentage × 360°, so 25% fills 90°. A pie shows proportions only, never totals: when comparing two pies, a bigger sector does not mean more people — read each chart's total as well.
4. Line graphs: trends over timeA line graph connects data points with a line to show change over time — for 'how it changes' questions. January to March temperatures: Jan 10°C, Feb 12°C, Mar 15°C; the rising line means the weather warms month by month.
   
   [[CHART:line:10,12,15]]
   
   The steepness of each segment reflects the pace of change: the steeper the segment, the faster the change. The horizontal axis must be time or ordered data; segments only join the dots and do not assert intermediate values — mid-January is not necessarily 11°C.
5. How to read a bar chartA bar chart carries two axes: categories along the horizontal (Chinese, English, Maths) and quantities up the vertical (headcount). Read it in three steps: first scan the horizontal axis for the categories; second check the vertical scale for what each grid square is worth; third compare bar heights for the conclusion. Watch the scale: if each square stands for 5 people, a bar four squares tall means 20 people; if the scale does not start at 0, the visual gaps are exaggerated — verify the scale before judging.
6. How to read a pie chartIn a pie chart the whole circle represents 100% and each sector represents one part's share. Read it in three steps: first note each sector's percentage or category label; second check that all the percentages add up to 100%; third find the largest sector, which is the biggest category. If sectors are labelled with angles, convert: angle ÷ 360° × 100% = percentage, so a 90° sector holds 25%. When comparing two pies, remember the two totals may differ, so sector areas must not be compared directly.
7. Choosing the right chartEach chart has its role: compare quantities with a bar chart, show proportions with a pie chart, show change with a line graph. Applications: comparing subject numbers calls for a bar chart; each subject's share of yearly library loans calls for a pie; monthly temperature changes call for a line. The wrong choice buries the message: a week of temperatures drawn as bars works but trends less clearly than a line, while preferences drawn as a line is plainly wrong, because categories have no order. In answers, name the chart type first and then the reason — both parts make a complete answer.

4Diagrams Diagrams

5Worked example Example

6Common mistakes Mistakes

7Quick check Quick check

8Recap Recap

• Chart: draw data visually
• Bar chart: compare quantities
• Pie chart: show proportions
• Line graph: show changes
• Read chart: title + axes + scale