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Describing Data

Describing Data. Statisticians describe a set of data in two general ways. First, they compute a measure of central tendency or the one number that is most typical of the entire set of data. Second, they describe the variation , or spread within the data. Measures of Central Tendency.

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Describing Data

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  1. Describing Data • Statisticians describe a set of data in two general ways. • First, they compute a measure of central tendency or the one number that is most typical of the entire set of data. • Second, they describe the variation, or spread within the data.

  2. Measures of Central Tendency • 3 different measures of central tendency are available: • Mean • Median • Mode • Measure of Central Tendency – the one number that is most typical for the set of data.

  3. Measures of Central Tendency • Mean – the arithmetic average or the sum of the individual values divided by the number of cases. • Median – the middle value, after all of the cases have been rank ordered from highest to lowest. • Mode – the value of the variable that occurs most often.

  4. Measures of Variation • Simple measures of variation are the range for a set of quantitative data and the frequency distribution for a set of qualitative data. • Range – computed by finding the difference between the smallest (minimum) and the largest (maximum) measures of the dependent variable.

  5. Frequency Distribution • The variation (qualitative data) is described through a frequency distribution that depicts the number of cases falling into each category of the variable. • For example: • the leaf quality of tomatoes produced with different concentrations of chemical X.

  6. General Data Table for Descriptive Statistics Level 1 Level 2 Level 3

  7. The Effect of Various Concentrations of Chemical X on the Height of Tomato Plants

  8. The Effect of Various Concentrations of Chemical X on the Health of Tomato Plants

  9. The Effect of Various Concentrations of Chemical X on Leaf Quality

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