Solved – How many measurements are needed to ‘baseline’ a measurement

Question

When we are monitoring movements of structures we normally install monitoring points onto the structure before we do any work which might cause movement. This gives us chance to take a few readings before we start doing the work to 'baseline' the readings.

Quite often the data is quite variable (the variations in the reading can easily be between 10 and 20% of the fianl movement). The measurements are also often affected by the environment in which they are taken so one set of measurements taken on one project may not have the same accuracy as measurements on another project.

Is there any statisitcal method, or rule of thumb that can be applied to say how many baseline readings need to be taken to give a certain accuracy before the first reading is taken? Are there any rules of humb that can be applied to this situation?

Answer 1

I think you should look at power calculations. These are often used to decide the sample size of survey or clinical trial. Taken from wikipedia:

A priori power analysis is conducted prior to the research study, and is typically used to determine an appropriate sample size to achieve adequate power.