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Z-scores A z-score or standardised score looks at how many standard deviations a score is above or below the mean.

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Presentation on theme: "Z-scores A z-score or standardised score looks at how many standard deviations a score is above or below the mean."— Presentation transcript:

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2 Z-scores A z-score or standardised score looks at how many standard deviations a score is above or below the mean.

3 Z-scores x-scale 0123 11 22 33 z-scale

4 Example 1 Kathini drinks strawberry milk each morning. She drinks an average of 340ml each morning with a standard deviation of 10ml. a) What is the z-score on a morning she drinks: i) 330mlii) 356ml b) What could you say about a day she drinks 371ml? a i)a ii) b) A z-score of 3·1 lies in the top 0·15% of the mornings. This may be considered an outlier, (maybe she drinks too much milk!)

5 Example 2 a) Sarah got a z-score of 2·1 on a test. What does this mean? b) This means that her score was 2·1 standard deviations above the mean. b) Aidan got a z-score of 1·7 on a test with a mean of 60%. If his mark was 94%, what was the standard deviation? c) Tim got a z-score of -1·3 on a test with a mark of 57%. If the standard deviation 10%, what was the mean mark? c)

6 Today’s work Exercise Sheet Q1→5 & 10


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