Use an Online Calculator for Complicated Error-Propagation Expressions
Statpages calculates how precision propagates through almost any expression involving one or two variables. It even handles the case of two variables with correlated fluctuations. You simply enter the following items:
The values of the variable or variables
The corresponding SEs
Consider the example of estimating the SE of the area of a circle whose diameter is 2.3 cm, with a SE of 0.2 cm. The formula for the area of a circle, in terms of its diameter (d) is A = (π/4)r2
The same web page can also analyze error propagation through expressions involving two measured values. Suppose you want to calculate body mass index (BMI, in kilograms per square meter) from a measured value of height (in centimeters) and weight (in kilograms), using the formula: BMI = 10,000weight/height2.
Suppose the measured height is 175 ± 1 centimeter, and the weight is 77 ± 1 kilograms (where the ± numbers are the SEs). The BMI is easily calculated as 10,000 x 77/1752, or 25.143 kg/m2. But what’s the SE of that BMI?
The problem would be entered into the web page as: