Don’t worry if you can’t remember how to calculate the Margin of Error (MOE) for a sum of values or the MOE for a derived ratio. The Cornell University Program on Applied Demographics has developed a simple easy-to-use online tool that will calculate the MOEs for sums, products, differences, ratios, and proportions. It will also calculate whether two values from the American Community Survey (ASC) are significantly different.
If you remember that MOEs are important, but don’t really remember what they are, check out this presentation (PDF) by the U.S. Census for all levels of users including those who last attetnded a statistics class in the last millennium.
One shortcoming of this tool is the fact that it can only calculate MOEs for two values. If you need the MOE for a list three or more values, try another another online calculator developed by the Oklahoma Department of Commerce.