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Measures of central tendency and dispersion

Measures of central tendency and dispersion. Measures of central tendency. Mean Median Mode ie finding a ‘typical’ value from the middle of the data. You need to be able to:. Explain how to calculate the mean, median and mode State the strengths and weaknesses of mean, median and mode

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Measures of central tendency and dispersion

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  1. Measures of central tendency and dispersion

  2. Measures of central tendency • Mean • Median • Mode • ie finding a ‘typical’ value from the middle of the data.

  3. You need to be able to: • Explain how to calculate the mean, median and mode • State the strengths and weaknesses of mean, median and mode • This could include saying which one you would use for some data e.g. 2, 2, 3, 2, 3, 2, 3, 2, 97 - would you use mean or median here?

  4. Advantages and disadvantages

  5. Measures of Dispersion • Measures of ‘spread’ • This looks at how ‘spread out’ the data are. • Are the scores similar to each other (closely clustered), or quite spread out?

  6. Range and standard deviation • The range is the difference between the highest and lowest numbers. What is the range of … • 3, 5, 8, 8, 9, 10, 12, 12, 13, 15 • Mean = 9.5 range = 12 (3 to 15) • 1, 5, 8, 8, 9, 10, 12, 12, 13, 17 • Mean = 9.5 range = 16 (1 to 17) • Example from Cara Flanagan, Research Methods for AQA A Psychology (2005) Nelson Thornes p 15

  7. Standard deviation • Standard deviation tells us the average distance of each score from the mean. • 68% of normally distributed data is within 1 sd each side of the mean • 95% within 2 sd • Almost all is within 3 sd

  8. Example • Mean IQ = 100, sd = 15 • What is the IQ of 68% of population (ie what is the range of possible IQs)? • Between what IQ scores would 95% of people be? • Dan says he has done an online IQ test, and he has an IQ of 170. Should you believe him? Why/not?

  9. Another example • Sol scores 61% in the test. His mum says that’s rubbish. Sol points out that the mean score in class was 50%, with an sd of 5. Did he do well? • What if the sd was only 2? • What if sd was 15?

  10. Advantages and disadvantages I used Cara Flanagan’s (2005) Research Methods for AQA A Psychology Nelson Thornes in preparing these slides.

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