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Mean, Median, Mode

Mean, Median, Mode. These are measures of central tendency All three give us information about a sample But some are more meaningful depending on the level of measurement. Which measure of central tendency do you use with…. Nominal level measure? Ordinal level measure Interval level measure

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Mean, Median, Mode

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  1. Mean, Median, Mode • These are measures of central tendency • All three give us information about a sample • But some are more meaningful depending on the level of measurement

  2. Which measure of central tendency do you use with… • Nominal level measure? • Ordinal level measure • Interval level measure • Ratio level measure

  3. Measures of Variability or Dispersion Range - high and lows. • Limitations: Based on only two extreme observations Interquartile range - measures variability based on percentiles. Q3(75th percentile) -Q1 (25th percentile) Limitations: Leaves out many observations Variance - Based on distances from the mean (X - mean). Takes the square of each deviation from the average and then averages the squares. ∑(x-µ)2 / n StandardDeviation - the square root of the variance

  4. Variance Formula How do we calculate the standard deviation?

  5. SPSS • SPSS uses the n-1 to calculate variance and standard deviation • This is important because if you use the raw-score formula (Box 4.2), you’ll get a slightly different answer. • If you use Box 4.1 and use n-1 instead of just N you get the same answer as SPSS

  6. Homework #3 • For homework #3 use the n-1 formula to calculate the variance and standard deviation. • This will allow you to use SPSS to check your hand calculations

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