Once you have developed the frequency and cumulative frequency distribution tables, you are ready to graph this information. Two graphs that summarize numerical data are histograms and ogives.
HISTOGRAM
A histogram is a graph that consists of vertical bars constructed on a horizontal line that is marked off with intervals for the variable being displayed. The intervals correspond to those in a frequency distribution table. The height of each bar is proportional to the number of observations in that interval. The number of observations can be displayed above the bars.
OGIVE
An ogive, sometimes called a cumulative line graph, is a line that connects points that are the cumulative percentage of observations below the upper limit of each class in a cumulative frequency distribution.
Symmetry
The shape of a histogram is said to be symmetric if the observations are balanced, or approximately evenly distributed, about the middle of the histogram.
Skewness
A distribution is skewed, or asymmetric, if the observations are not symmetrically distributed on either side of the middle. A positively skewed distribution has a tail that extends to the right, in the direction of positive values. A negatively skewed distribution has a tail that extends to the left, in the direction of negative values.
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