2: Data Displays
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- 2.1: Data, Sampling, and Variation in Data and Sampling
- Data are individual items of information that come from a population or sample. Data may be classified as qualitative, quantitative continuous, or quantitative discrete. Because it is not practical to measure the entire population in a study, researchers use samples to represent the population. A random sample is a representative group from the population chosen by using a method that gives each individual in the population an equal chance of being included in the sample.
- 2.2: Histogram
- Graphical representations of large data sets provide a quick overview of the nature of the data. A population or a very large data set may be represented by a smooth curve. This curve is a very fine relative frequency histogram in which the exceedingly narrow vertical bars have been omitted. When a curve derived from a relative frequency histogram is used to describe a data set, the proportion of data with values between two numbers a and b is the area under the curve between a and b, as
- 2.3: Stem-and-Leaf Graphs (Stemplots), Line Graphs, and Bar Graphs
- A stem-and-leaf plot is a way to plot data and look at the distribution, where all data values within a class are visible. The advantage in a stem-and-leaf plot is that all values are listed, unlike a histogram, which gives classes of data values. A line graph is often used to represent a set of data values in which a quantity varies with time. These graphs are useful for finding trends. A bar graph is a chart that uses either horizontal or vertical bars to show comparisons among categories.