2 Organizing Data
Definition: Discrete Variable
A quantitative variable whose possible values form a finite (or countably infinite) set of numbers.
Definition: Continuous variable
A quantitative variable whose possible values form some interval of numbers.
Definition: Data
Information obtained by observing values of a variable.
Definition: Qualitative data
Data obtained by observing values of a qualitative variable.
Definition: Quantitative data
Data obtained by observing values of a quantitative variable
Definition: Discrete data
Data obtained by observing values of a discrete variable.
Definition: Continuous data
Data obtained by observing values of a continuous variable.
Definition: Distribution of a data set
a table, graph, or formula that provides the values of observations and how often they occur.
Definition: Classes
Categories for grouping data.
Definition: Frequency
The number of observations that fall in a class.
Definition: Frequency distribution
A listing of all classes along with their frequencies.
Definition: Relative frequency
The ratio of the frequency of a class to the total number of observations.
Definition: Relative-frequency distribution
A listing of all classes along with their relative frequencies.
Definition: Lower cutpoint
The smallest value that can go in a class.
Definition: Upper cutpoint
The smallest value that can go in the next higher class. The upper cutpoint of a class is the same as the lower cutpoint of the next higher class.
Definition: Midpoint
The middle of a class, obtained by taking the average of its lower and upper cutpoints.
Definition: Width
The difference between the upper and lower cutpoints of a class.
Definition: Grouped data table
a table that provides the classes, frequencies, relative frequencies, and midpoints of a data set.
Definition: Frequency histogram
A graph that displays the classes on the horizontal axis and the frequencies of the classes on the vertical axis. The frequency of each class is represented by a vertical bar whose height is equal to the frequency of the class.
Definition: Relative-frequency histogram
A graph that displays the classes on the horizontal axis and the relative frequencies of the classes on the vertical axis. The relative frequency of each class is represented by a vertical bar whose height is equal to the relative frequency of the class.
Common distribution shapes
Definition: Population distribution or the distribution of the variable
The distribution of the population data.
Definition: Sample distribution
The distribution of sample data.
Theorem:
The distribution of a random sample from a population approximates the population distribution. In other words, if a random sample is taken from a population, then the distribution of the observed values of the variable under consideration will approximate the distribution of the variable. The larger the sample, the better the approximation tends to be.
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