Lesson L4

L4 Outliers and cleaning data Quiz: AQA Maths, Unit 11

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson L4, Outliers and cleaning data: 20 multiple choice questions for the AQA Maths (7357), Unit 11: Statistics, written with Revision Ninja.

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The 20 questions

  1. What is an outlier in a data set?

    • The mean of the data
    • A value that lies unusually far from the rest of the data
    • The most common value
    • A value exactly equal to zero

  2. Using the 1.5 times IQR rule, what defines an outlier?

    • Any value different from the mean
    • The largest and smallest values always
    • A value more than 1 IQR above the median
    • A value more than 1.5 times the IQR below Q1 or above Q3

  3. What is a sensible first step when some values are missing in a data set?

    • Ignore the missingness entirely
    • Replace every missing value with zero
    • Investigate why they are missing before deciding whether to remove, estimate or record them
    • Delete the whole data set

  4. A data value looks much larger than the others and appears to be a typing error. What should be done?

    • Keep it because all data must be kept
    • Add more values to dilute its effect
    • Check the source and correct it if a recording error is confirmed
    • Replace all values with the mean

  5. What is the main effect of an outlier on the mean?

    • It removes the mode
    • It makes the range zero
    • It changes the median a lot
    • It pulls the mean towards the outlier

  6. For the data 3, 5, 6, 7, 8, 9 and 40, which value is an outlier using the 1.5 IQR rule?

    • 3
    • 8
    • 9
    • 40

  7. For the data 3, 5, 6, 7, 8, 9 and 40, what is the mean including all values, to 1 decimal place?

    • 11.1
    • 7.0
    • 78
    • 6.3

  8. For the data 3, 5, 6, 7, 8, 9 and 40, what is the mean after removing the outlier 40, to 1 decimal place?

    • 6.3
    • 7.0
    • 9.0
    • 11.1

  9. For the data 3, 5, 6, 7, 8, 9 and 40, what is the median after removing the outlier 40?

    • 6.5
    • 7
    • 6
    • 7.5

  10. In a survey of 50 responses, 5 are missing a height value. What is the best first step?

    • Discard all 50 responses
    • Treat the missing values as zero
    • Check whether the missing values are random or related to other variables before choosing how to handle them
    • Substitute the mean without checking

  11. A dataset of adult heights recorded in metres contains the value 170. What is the most sensible action?

    • Increase the sample size to dilute it
    • Replace all heights with the mean
    • Keep it because it is a data value
    • Check the source and correct it if a recording error is confirmed, for example to 1.70 m

  12. Which type of diagram is best for showing outliers in a data set?

    • A time series of the mean only
    • A frequency table of categories only
    • A pie chart
    • A box plot

  13. A genuine but extreme value is found in a data set of 200 values. What should be done?

    • Replace it with the median silently
    • Convert it to zero
    • Delete it silently
    • Keep it in the data, and report results with and without it while explaining the effect

  14. Quartiles Q1 = 12 and Q3 = 20 are found for a data set. What is the upper fence for outliers?

    • 28
    • 32
    • 24
    • 36

  15. With Q1 = 12 and Q3 = 20, which of these values is an outlier?

    • 10
    • 25
    • 30
    • 33

  16. What effect does an outlier usually have on the standard deviation?

    • It changes the median to the outlier value
    • It has no effect on the standard deviation
    • It decreases the standard deviation
    • It increases the standard deviation substantially

  17. An exam mark out of 100 is recorded as 105. What is the correct action?

    • Accept it because it is above average
    • Round it to 100 without checking
    • Treat it as an error, check the source, and correct it since marks cannot exceed the maximum
    • Remove the whole class from the data

  18. Why are the median and interquartile range useful for skewed data with outliers?

    • They ignore all the data
    • They are always larger than the mean and SD
    • They are resistant to extreme values, so they summarise typical values better
    • They are only valid for normal data

  19. A data set is 1, 2, 3, 4 and 100. Which statement best describes the effect of the value 100?

    • It has no effect on the mean
    • It makes the median equal to 100
    • It makes the mean smaller than 1
    • It makes the mean much larger than the median, so the mean is misleading

  20. When outliers are removed from a data set, what must be reported?

    • Nothing, since removal is always justified
    • That outliers were removed, why they were removed, and how many values were removed
    • The mean of the outliers only
    • Only the outliers, not the rest of the data

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