2.5 Data Analyses 
The use of a probability based sampling design allows the development of 
estimates of the extent of area, with 95% confidence intervals, of the intertidal resource 
that has any given observed indicator value. Analysis of indicator data was conducted 
by calculation of cumulative distribution functions (CDFs), an analysis approach that has 
been used extensively in other EMAP/NCA coastal studies (Summers et al. 1993, 
Strobel et al. 1995, Hyland et al. 1996, U.S. EPA 2004, 2006). A detailed discussion of 
methods for calculation of the CDFs used in EMAP analyses are provided in Diaz- 
Ramos et al. (1996). 
Data are presented in this report in several graphical forms. Comparisons 
among the three states Washington, Oregon, and California, the intensive study in San 
Francisco Bay, and the values for the entire Western intertidal region (omitting the high 
marsh samples from San Francisco Bay), are presented as bar charts of average 
values for the five categories plus 1 standard deviation as an estimate of error. Where 
there existed reasonable benchmarks to assign condition assessments to an indicator, 
estimates of the percentage area of the intertidal zone within the condition levels is 
provided in the text. 
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