Unit 1 Chapter 3

Histogram

A bar graph of a frequency or relative frequency distribution in which the height of each bar corresponds to the frequency or relative frequency of each class. In other words, a histogram is the graph of a frequency distribution for quantitative data. Each of the classes in the frequency distribution is represented by a vertical bar whose height is proportional to the frequency of the interval. The horizontal boundaries of each vertical bar corresponds to the class boundary.

Time Series Plot

A graph of time series data that you can use to evaluate patterns and behavior in data over time. Most often, a time series plots come in the form a a line graph, which connects consecutive points over time. It displays observations on the y-axis against equally spaced time intervals on the x-axis.In other words, time is always labeled on the horizontal axis, with the variable being measured labeled on the vertical axis. Points are then plotted for each time period, and a line is drawn that connects each consecutive point. These plots are often used to examine daily, weekly, seasonal or annual variations, or before-and-after effects of a process change. They are especially useful for comparing data patterns of different groups. Line graphs can be analyzed with or without each point being visible.

Dot Plot

A graph where each data value is plotted as a point, or a dot, above a horizontal axis. If there are multiple entries of the same data value, they are plotted one above another. Dot plots are useful when you are interested in where the data are clustered and which values occur most often.

Bar Chart

A simple graphical display in which the length of each bar corresponds to the number of observations in a category. Bar charts are often used to illustrate a frequency distribution for qualitative data. Unless there is a good reason, the axis used to measure the bars should start at zero, otherwise the axis can be stretched to exaggerate differences in the bar lengths. Bar charts must include axis labels and a title.

Stem-and-Leaf Displays

A stem-and-leaf display is a table where each data value is split into a "stem" and a "leaf". The "stem" is the first digit or digits of a data point and is listed down. The "leaf" values go either right or left from the stem values and are usually the last digit. All of the data values that have common stems are group together, and their leaves branch out from the common stem. The leaf unit represents which decimal place the leaf values represent. Stem-and-leaf plots are appropriate for small discrete data sets. They are useful for both ordering and detecting patterns in the data. Similarly, you can find the median of the data fairly easily using a stem-and-leaf display because the plot shows exact data points.

Cumulative Relative Frequency Distribution

Cumulative relative frequency is the proportion of observations in a particular class and all preceding classes. To obtain the cumulative relative frequency, add the relative frequencies of all previous classes to the relative frequency of the current class.

Frequency Distribution

Frequency is the number of times a data value occurs. A frequency distribution table summarizes data into classes and provides in tabular form a list of the classes along with the number of observations in each class. Whether data is qualitative or quantitative affects the categories used when displaying the data in tabular form. With the frequency distribution, we are able to see the broader structure of data. The purpose of the frequency distribution is to condense the set of data into a meaningful summary form.

Pie Chart

Pie charts can also be sued as a means of expressing frequency distributions. The circle represents the total "pie" available, and the slices are proportional to the amount in each category. One advantage of the pie chart is the ability to easily compare the total in each of the classifications to the total number of observations.

Relative Frequency Distribution

Relative frequency represents the proportion of the total observations in a given class. A relative frequency distribution table enables the reader to view the number in each category in relation to the total number of observations. Converting the frequency in each class to a proportion in each class enables us to compare data sets with different numbers of observations.

Stacked Bar Chart

Stacked bar chars are variations on the standard bar chart that are used for grouping or categorizing the parts of a whole. Stacked bar charts are useful when there are three components to the data. The bars in the chart are categorized into stacking order to represent different values. One axis will show the discrete value and the other will provide the variable bars in a stacking order. Different colors show the distinctive parts of the whole bar.