![]() The interquartile range, or IQR, is the range of the middle 50 percent of the data values. The first quartile ( Q 1) is the 25 th percentile, the second quartile ( Q 2 or median) is the 50 th percentile, and the third quartile ( Q 3) is the 75 th percentile. For example, an observation at the 50 th percentile would be greater than 50 percent of the other observations in the set. Percentiles are used to compare and interpret data. The values that divide a rank-ordered set of data into 100 equal parts are called percentiles. Time series graphs can be helpful when looking at large amounts of data for one variable over a period of time. The data usually go on the y-axis with the frequency being graphed on the x-axis. A frequency polygon can also be used when graphing large data sets with data points that repeat. Histograms are typically used for large, continuous, quantitative data sets. The heights of the bars correspond to frequency values. The horizontal scale represents classes of quantitative data values, and the vertical scale represents frequencies. The graph consists of bars of equal width drawn adjacent to each other. ![]() ![]() 2.2 Histograms, Frequency Polygons, and Time Series GraphsĪ histogram is a graphic version of a frequency distribution. Bar graphs are especially useful when categorical data are being used. One axis of the chart shows the specific categories being compared, and the other axis represents a discrete value. A bar graph is a chart that uses either horizontal or vertical bars to show comparisons among categories. ![]() These graphs are useful for finding trends, that is, finding a general pattern in data sets, including temperature, sales, employment, company profit, or cost, over a period of time. A line graph is often used to represent a set of data values in which a quantity varies with time. The advantage in a stem-and-leaf plot is that all values are listed, unlike a histogram, which gives classes of data values. In a stem-and-leaf plot, all data values within a class are visible. 2.1 Stem-and-Leaf Graphs (Stemplots), Line Graphs, and Bar GraphsĪ stem-and-leaf plot is a way to plot data and look at the distribution. ![]()
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