Define the choice that needs to be made between two options. If more than two options are involved in the decision, then you will have to split the decision into two or more separate decisions. A public policy example might be where to put a landfill. Since there are usually several potential places to put a landfill, list the choices for each potential spot separately.
List all variables that may apply to the decision. In the above example, this might include cost, proximity to residential areas, proximity to water sources and political opposition. Be sure to include any variables that would make the outcome impossible or extremely undesirable.
Convert all variables to true or false statements, such as "No political opposition." Since some of the variables may have numeric values, you may need to reword them. For example, you may reword the cost of locating the site at a particular spot as "Cost < 2 million $." You may reword the proximity variables as "Residential proximity > 1 mile" and "Water proximity > 1 mile."
Set up the equation. The equation for the example might be "If 'no political opposition,' and 'cost < 2 million $,' and 'residential proximity > 1 mile,' and 'water proximity > 1 mile,' then 'choose site 1'."
Determine whether the statements are true or false. In the example, if all of the requirements to the left of the word "then" are true, then choose site one. If any of the statements are false, then discard site one and consider the next site.