![]() We will illustrate it using the same data set from the previous subsection. A frequency histogram A graphical device showing how data are distributed across the range of their values by collecting them into classes and indicating the number of measurements in each class. The stem and leaf diagram is not practical for large data sets, so we need a different, purely graphical way to represent data. There are two perfect scores three students made scores under 60 most students scored in the 70s, 80s and 90s and the overall average is probably in the high 70s or low 80s. Either way, with the data reorganized certain information of interest becomes apparent immediately. The display is made even more useful for some purposes by rearranging the leaves in numerical order, as shown in Figure 2.2 "Ordered Stem and Leaf Diagram". Thus the three leaves 9, 8, and 9 in the row headed with the stem 6 correspond to the three exam scores in the 60s, 69 (in the first row of data), 68 (in the third row), and 69 (also in the third row). The number in the units place in each measurement is a “leaf,” and is placed in a row to the right of the corresponding stem, the number in the tens place of that measurement. The numbers in the tens place, from 2 through 9, and additionally the number 10, are the “stems,” and are arranged in numerical order from top to bottom to the left of a vertical line. One way to do so is to construct a stem and leaf diagram as shown in Figure 2.1 "Stem and Leaf Diagram". However the data set may be reorganized and rewritten to make relevant information more visible. How did the class do on the test? A quick glance at the set of 30 numbers does not immediately give a clear answer. Bar graphs are especially useful when categorical data is being used.Suppose 30 students in a statistics class took a test and made the following scores: 86 80 25 77 73 76 100 90 69 93 90 83 70 73 73 70 90 83 71 95 40 58 68 69 100 78 87 97 92 74 Some bar graphs present bars clustered in groups of more than one (grouped bar graphs), and others show the bars divided into subparts to show cumulative effect (stacked bar graphs). ![]() 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. That is, finding a general pattern in data sets including temperature, sales, employment, company profit or cost over a period of time. These graphs are useful for finding trends. 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. The frequency points are connected using line segments.Ī stem-and-leaf plot is a way to plot data and look at the distribution. In the particular line graph shown in Example, the x-axis (horizontal axis) consists of data values and the y-axis (vertical axis) consists of frequency points. It takes some background information to explain outliers, so we will cover them in more detail later.Īnother type of graph that is useful for specific data values is a line graph. ![]() Some outliers are due to mistakes (for example, writing down 50 instead of 500) while others may indicate that something unusual is happening. When you graph an outlier, it will appear not to fit the pattern of the graph. An outlier is an observation of data that does not fit the rest of the data. You want to look for an overall pattern and any outliers. The stemplot is a quick way to graph data and gives an exact picture of the data. \right)\) were in the 90s or 100, a fairly high number of As.įor the Park City basketball team, scores for the last 30 games were as follows (smallest to largest):ģ2 32 33 34 38 40 42 42 43 44 46 47 47 48 48 48 49 50 50 51 52 52 52 53 54 56 57 57 60 61Ĭonstruct a stem plot for the data.
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