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Published byNathan Hill Modified over 8 years ago

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Describing Data Statisticians describe a set of data in two general ways. 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.

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Measures of Central Tendency 3 different measures of central tendency are available: 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.

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Measures of Central Tendency Mean – the arithmetic average or the sum of the individual values divided by the number of cases. 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. 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. Mode – the value of the variable that occurs most often.

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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. 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. Range – computed by finding the difference between the smallest (minimum) and the largest (maximum) measures of the dependent variable.

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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. 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.

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General Data Table for Descriptive Statistics Title: The Effect of the ____________ on the ____________. Descriptive Information Independent Variable Central Tendency Variation Number Level 1 Level 2 Level 3

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The Effect of Various Concentrations of Chemical X on the Height of Tomato Plants Descriptive Information Concentration of Chemical X (%) 0 10 20 30 Mean Range Maximum Maximum Minimum Minimum Number

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The Effect of Various Concentrations of Chemical X on the Health of Tomato Plants Concentration of Chemical X (5) Descriptive Information 0 10 10 20 20 30 30 Mode Frequency Distribution Healthy Healthy Unhealthy Unhealthy Number

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The Effect of Various Concentrations of Chemical X on Leaf Quality Concentration of Chemical X (%) Descriptive Information 0 10 10 20 20 30 30 Median Frequency Distribution Quality 4 Quality 4 Quality 3 Quality 3 Quality 2 Quality 2 Quality 1 Quality 1 Number

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