Statistics

Every day you see statistics: opinion polls before an election, news stories about screen time, sports commentators comparing players. In this topic you'll learn how data is collected, how to choose a display that tells the truth about it, and how to compare two groups by looking at their centre, spread and shape. You'll also learn to read reports in the media with a careful eye, and finish by planning and running a statistical investigation of your own.

What you'll learn

• 11.01 Types of data: categorical and numerical data, primary and secondary data, census or sample, sampling methods, and how bias creeps into a survey.
• 11.02 Data displays: frequency tables, dot plots, column graphs and sector graphs, choosing the right display, and spotting graphs that mislead.
• Investigation: opinion polls. How polls are run, what the margin of error means, and why a sample of 1000 people can tell you about millions.
• 11.03 Back-to-back stem and leaf: drawing and reading back-to-back stem-and-leaf plots to compare two groups.
• 11.04 Grouped histograms: grouping data into class intervals, drawing histograms, finding the modal class and estimating the mean.
• 11.05 Shape of data: symmetrical and skewed data, one peak or two, clusters, gaps and outliers, and how outliers change the mean, median and range.
• Investigation: statistical reports in the media. Read a news report like a statistician: how was the data collected, and do the numbers and graphs really support the headline?
• 11.06 Compare data sets: comparing two groups using the mean, median, range and IQR, and writing a clear conclusion.
• Investigation: plan and conduct a statistical investigation. Ask a question that compares two groups, collect and analyse the data, and decide how strong your evidence is.

Which level should I pick?

Every worksheet comes in three levels. Each one covers the same skills.

• Level 1 · Warm-up: smaller data sets, whole numbers and more help along the way. A good place to start.
• Level 2 · Core: the main worksheet for the lesson.
• Level 3 · Challenge: decimals, working backwards, missing values and problems with more steps and more explaining, for when the Core level feels easy.

Not sure? Start with Level 2. If the first few questions feel tricky, drop to Level 1. If you finish quickly and get them right, try Level 3. Download the worksheet, print it, and write your answers in the boxes.

Practice tests

When you've finished the lessons, try the three practice tests. Each one is like the real topic test: 45 minutes, 40 marks, a section without a calculator and a section with one. Write your working under each question, then copy your final answers onto the answer sheet on the last page, just like you will in the real test.