Then, you can plot the points at the top of each bar and connect them with lines to create the polygon. The x-axis of the frequency polygon represents the values or intervals of the data, and the y-axis represents the frequencies. To create a frequency polygon, you need to first create a frequency table that shows the number of observations (frequencies) for each value or interval of values in the data. It is similar to a histogram, but instead of using bars to represent the frequencies, it uses lines that connect the points at the top of the bars. Frequency Polygonsįrequency polygons display the distribution of quantitative data by using lines and connecting points at the midpoints of the classes for each bin. Remember, always check the quantitative data assumption to verify the right graph or display. The height of bins represents the frequencies of the classes. If there is a space, then that indicates an actual gap in data with no values. Unlike the bar graphs, there is no space between histogram bins. The width of the bars represents the interval width, and the x-axis represents the values of the data. The bins are created by dividing the range of the data into equal-width intervals, and the height of each bar in the histogram corresponds to the number or proportion of observations that fall within the interval represented by that bar. HistogramsĪ histogram is a graphical representation of a distribution of data, where the data is divided into piles called bins. The main displays we will discuss are histograms, polygons, ogive, stem-and-leaf plots, and dot-plot. Just know that many computer programs, including our mighty Microsoft Excel, and your TI series calculator can make it in seconds. The good news is that AP doesn’t require you to make one from scratch, so we will skip this one. This time, we'll describe how we organize and display quantitative data. The frequency table is a bit complicated for quantitative data, especially if we deal with vast amounts of data. Other examples of continuous variables include the length of a piece of wood, the time it takes to run a marathon, and the temperature of a room. For example, it is not possible to count the number of possible values for height, because there are an infinite number of possible values between any two given values. No matter how small the interval between two values of a continuous variable, it is always possible to determine another value between them. □Ī continuous variable can take on infinitely many values, but those values cannot be counted. Examples of discrete variables include the number of children in a family or in a class, the number of cars in a parking lot, and the number of votes received by a political candidate in a mayoral election. The number of values may be finite or countably infinite, as with the counting numbers. Under quantitative variables are two mini-types:Ī discrete variable can take on a countable number of values. Remember from a previous section that quantitative variables refer to variables that can be measured or counted and have a numerical value.
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