• In a frequency distribution, the mode is interpreted strictly. • In the context of the form of a distribution, modality is interpreted more loosely.
Example : The form of (b) would be described as bimodal, even though it is clear that there is only one value for the mode Skewness • Skewness refers to the lack of symmetry of a distribution. • If you drew a vertical line down from the mode of the symmetrical distribution to the right, you would produce two identical halves. • If the halves are not identical, then the distribution is asymmetrical, or skewed. • A distribution may be positively or negatively skewed Kurtosis • Kurtosis refers to how peaked a distribution is. • It is possible for two distributions to be the same in terms of their modality and skewness and yet to differ in their kurtosis. • Distributions can be classified according to how peaked they are: • Leptokurtic : The distribution is very peaked, and variable scores are more tightly clustered. • Platykurtic : The distribution is flat, and variable scores are more widely dispersed.
• Mesokurtic : The distributions is moderately peaked, and variable scores are somewhat spread out. Charts and Graphs • Charts and graphs are visual displays of how the scores on a variable are distributed. • Charts and graphs do not provide new information about a distribution of variable values; rather, they simply display the information in pictorial form. • Pie charts begin with a circle that represents the entire distribution of scores on a variable. • Each wedge of a pie chart represents an attribute (category) of a variable, and the size of each wedge is proportional to the frequency of scores in that category as a percentage of all scores in that distribution (sample). • Effective pie charts generally have no more than about six wedges. • Bar charts can be used to illustrate information for a categorical variable.
- Fall '13
- Bar chart