Reading & Interpreting Statistical Diagrams (Edexcel IGCSE Maths)

Spec point — 6.1C

Reading & interpreting statistical diagrams

How do I interpret statistical diagrams?

• Read and understand the initial sentences describing the situation (context)

  • Underline important words if necessary

• Look for any keys that may help you to understand the diagram

  • For example

    • 1 unit represents 20 people
    • Year 10 is the solid line, Year 11 is the dotted line
    • Class A is shaded, class B is striped

• Read the titles of diagrams and all axes labels

  • A graph for 'new students at a school' is different to 'all students at the school'
  • A frequency axis that starts at 50 is different to one starting at 0

• Understand which units are being used

  • Individual lengths may be in centimetres but total length may be in metres
  • Populations may be measured in thousands

• Look out for any extreme values (outliers / anomalies)

  • One month's temperature might be unusually high

    • Was it a heat wave or a recording error?

How do I draw conclusions from diagrams?

• Look for overall trends in the diagram

  • Prices **increase **year on year
  • The temperature peaks in June

• Use** numbers** from the graphs

• Refer to any changes

  • The steepness (gradient) of graph may change

• Write in full sentences that copy the exact wording from the question

  • 'The number of goats in farm A has decreased by 12 over the 8 month period'
  • Not 'There are fewer of them now'

• You may need to calculate the mode, median, mean or range to support any explanations

• Understand why drawing conclusions may not be suitable

  • The data set may be too small to be representative

  • The data set may be biased

  • Consider the scope of the data

    • e.g. Data for January to March cannot be used to predict August

Worked Example The diagram below shows the temperature of a garden in the UK, recorded at 7am on each day of a particular week in March.

(a) Describe the change in temperature over the first four days.

Answer:

The trend shows a decrease in the first three days, then a constant temperature Find numbers from the graph to use in your answer Refer to the steepness of the change

Final answer: The temperature decreases from 12°C on Sunday to 9°C on Wednesday The decrease is steeper over the first two days There is then a constant temperature of 9°C on both Wednesday and Thursday

(b) A gardener claims that, based on the graph, Monday must have experienced the highest temperature that week.

Give a reason as to why this might not be true.

Answer:

Reread the information at the start These temperatures were recorded at 7am in the morning (we don't know how hot the rest of the day was)

Final answer: The temperatures on the graph are at 7am each day The maximum temperature may have been after 7am, on a day that was not Monday

(c) A journalist wants to use the data shown to claim that the average temperature that week was below 10°C. The mean of the temperatures shown is 10°C.

Which type of average would you suggest they use? Explain your answer.

Answer:

The mean of 10°C does not support the claim that the average temperature is below 10°C Try calculating the mode instead

12, 10, 9, 9, 11, 10, 9

The most frequent number is 9

Final answer: The modal temperature is 9°C 9°C < 10°C so using the mode would help the journalist's claim