Statistical tests can be classified into 5 types, based on the measurement scales of your response and explanatory variables. Are those scales continuous, or grouped?
Response variable
the variable you are trying to
understand
usually plotted on the Y axis
continuous (1.4, 2.5, ...) or
grouped (above vs.
below detection limit)
Explanatory variables
variables used to explain Y
usually plotted on the X axis
continuous (1.4, 2.5, ...) or
grouped (ag,
urban, forest)
Choose (click on) your procedure based on whether your variables are continuous or grouped:
.
Continuous Y 
Grouped X
Compare differences among two or
more groups
Continuous Y 
Continuous X
Relate a continuous Y variable to one
or more continuous explanatory variables.
Continuous Y 
both Grouped and Continuous X
Is there 1 or more than 1 regression
line?
Grouped Y 
Grouped X
Do percentages of Y categories
(detect / nondetect) change between two or more groups
(June vs. Sept)?
Grouped Y 
Continuous X
Do percentages (% hits) change
as one or more explanatory variables (thickness)
change?