Lecture Notes Chapter Two: Methods for Describing Sets of Data Randall Miller1 | P a g e 1.Describing Qualitative Data Definition 2.1 A classis one of the categories into which qualitative data can be classified. Definition 2.2 The class frequencyis the number of observations in the data set that fall into a particular class. Definition 2.3 The class relative frequencyis the class frequency divided by the total number of observations in the data set; that is, class frequencyclass relative frequencyn=Definition 2.4 The class percentageis the class relative frequency multiplied by 100; that is, ()class percentageclass relative frequency*100=Summary of Graphical Descriptive Methods for Qualitative DataBar Graph: The categories (classes) of the qualitative variable are represented by bars, where the height of each bar is either the class frequency, class relative frequency, or class percentage. Pie Chart: The categories (classes) of the qualitative variable are represented by slices of a pie (circle). The size of each slice is proportional to the class relative frequency. Pareto Diagram: A bar graph with the categories (classes) of the qualitative variable (i.e., the bars) arranged by height in descending order from left to right. 2.Graphical Methods for Describing Quantitative Data Determining the Number of Classes in a Histogram Number of Observations in Data Set Number of Classes Fewer than 25 5 – 6 25 - 50 7 – 14 More than 50 15 - 20 Summary of Graphical Descriptive Methods for Quantitative Data Dot Plot: The numerical value of each quantitative measurement in the data set is represented by a dot on a horizontal scale. Then data values repeat, the dots are placed above one another vertically.
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