GCSE · Scatter graphs & correlation

Scatter graphs & correlationExam-style questions

Why one point on a scatter graph is one individual measured twice, how to describe correlation by type and strength in the words of the question, why a correlation never proves a cause, and how to place a line of best fit — through the bulk of the data, balanced either side, ignoring a genuine outlier.

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10 questions · GCSE (Higher) level · mark scheme and worked solution on each · no sign-up to try

DifficultyAllLevel 1Level 2Level 3Level 4Level 5
  1. 1
    A researcher recorded, for each of 1212 secondary schools, the number of computers the school owns and the total number of GCSE passes gained by its pupils last summer. The scatter graph shows the results.20406080100120140160100200300400500600700Number of computersNumber of GCSE passesA local newspaper printed the headline: "Buying more computers raises GCSE results."

    Explain why the researcher's data does not support this headline. You must refer to the scatter graph in your answer.
    Level 4 · 3 marksTry it
  2. 2
    A café recorded, for each of 88 weeks, the amount it spent on local advertising and the number of customers it served that week.

    Ben has drawn the straight line shown on the scatter graph and says it is his line of best fit.20406080100120140160100200300400500Spent on advertising (£)Number of customers(a) Give two reasons why Ben's line is not a good line of best fit.

    (b) Ben then says: "The correlation between the amount spent on advertising and the number of customers must be weak."

    Explain why Ben is wrong.
    Level 4 · 3 marksTry it
  3. 3
    In an experiment, 99 identical bean plants were each given a different mass of fertiliser. The table shows the mass of fertiliser, in grams, and the height of each plant, in centimetres, after four weeks.
    Fertiliser
    (g)    		Height after 4 weeks (cm)
    218
    424
    627
    833
    1038
    1225
    1447
    1651
    1857
    The scatter graph shows the same information.5101520102030405060Fertiliser (g)Height (cm)(a) One of the plants is an outlier. Write down the mass of fertiliser that this plant was given.

    (b) Give a possible reason why this plant does not fit the pattern.

    (c) Describe the correlation shown by the other eight plants.

    (d) Draw a line of best fit for the other eight plants on the scatter graph.
    Level 4 · 5 marksTry it