# Uncertainty in Measurement (Question)

1. Oct 1, 2009

### BAnders1

In regards to data analysis, what would it mean if you measured some quantity, say the speed of light for example, and you measured an average value that was 110% of the true value. If your uncertainty in measurement is LESS than 10%, does that mean that something is wrong with your data or experimental method?

In general, should the uncertainty in measurement create a "bubble" around the average measured value that always encloses the true value, given that your experimental method and theory is correct, and that you accounted for every possible error?

2. Oct 1, 2009

### Bob S

If you believe your data, and your estimate of statistical uncertainty, then the "true value" might be wrong. In my PhD thesis, I used a new and very precise method to measure a parameter that was previously measured by my thesis advisor 10 years earlier. My measurement was two (of his) standard deviations lower, and his was 30 (of my standard deviations) higher. My measurement turned out to be correct. (I got my PhD anyway.)
Bob S