Concept: Cochran-Armitage Test for Trend
Last Updated: 2008-09-05
The Cochran Armitage test is a method of directing chi squared tests toward narrow alternatives. The test is sensitive to the linearity between response variable and experimental variables and detects trends that would not be noticed by more crude methods.
When the linear probability model holds, the statistic z 2 , based on df = 1, tests for a linear trend in the proportions. The trend test may give strong evidence of positive or increasing linear trends, of constant or stable trends over time, or of negative or decreasing trends. Results of the trend test are similar to those obtained by testing that the slope is zero in a linear logit model.
In Roos et al. (1999), the trend statistic was used to measure the growth in screening mammography over time (an increasing linear trend) among both urban and rural women.
There are several web sites available that detail statistical information about the trend test and how to apply it using SAS® software. The following two sites are accessible from this page to assist in this description and to provide working examples of this statistical test:
SAS Code Example
The SAS® system provides procedures for calculating various "trend" statistics. One application of the Cochran Armitage trend test is an option within
. Specifying 'trend' within the
statement will generate the statistic.
/*Produce a cross tab with display of Cochran Armitage trend statistic*/
proc freq data= name_of_data ;
tables var1 * var2 /trend ;
- Agresti A. Categorical Data Analysis. New York,NY: John Wiley and Sons, Inc. 1990. 1-576.(View)
- Roos LL, Traverse D, Turner D. Delivering prevention: the role of public programs in delivering care to high-risk populations. Med Care 1999;37(6 Suppl):JS264-JS278. [Abstract] (View)
- data analysis
- logistic regression
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