Epidemiology and Biostatistics pp 153-162 | Cite as

# Summary Measures in Statisitics

## Learning Objectives

- 1.Three types of variables are commonly used in clinical research studies:
- (a)
Continuous – can take on an infinite number of possible values

- (b)
Binary – can take on only two possible values

- (c)
Categorical – can take on only a few possible values

- (a)
- 2.
A histogram plots the observed values of a variable on the

*X*-axis versus the relative frequency of these values on the*Y*-axis. - 3.
The arithmetic mean describes the middle of the data for symmetric distributions, including data from normal-appearing distributions.

- 4.
The median refers to the value within a distribution for which exactly half of the data fall above this value and half fall below it.

- 5.
Disagreement between mean and median values suggests that a distribution is

*not*normally distributed. - 6.
A continuous variable may be divided into 3, 4, or 5 equally sized groups called tertiles, quartiles, and quintiles, respectively.

- 7.
The interquartile range is defined as the 25th and 75th quantiles of a distribution.

- 8.
Some techniques to describe the joint distribution between two variables include tabulation across categories, scatter plots, correlation, and quantile-continuous plots.

- 9.Correlation coefficients are interpreted as:
- (a)
+1 indicates perfect positive agreement between two variables

- (b)
0 indicates no agreement between two variables

- (c)
–1 indicates perfect negative agreement between two variables

- (a)