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Random and Systematic Errors


Date: 03/05/2002 at 14:32:54
From: Richard
Subject: Random/Systematic Errors

Hello,

While reading a book I came across the terms 'random errors' and 
'systematic errors'. I don't understand the meanings of these two 
phrases. 

Thank you.


Date: 03/05/2002 at 16:44:41
From: Doctor Shawn
Subject: Re: Random/Systematic Errors

Thanks for writing to Dr. Math, Richard.

Systematic errors are easier to deal with. Imagine that you are taking 
weight measurements on a scale. The only problem is that the scale is 
broken, and adds a half pound to everything you measure with it.  
Obviously, this will skew your data. Fortunately for you, though, it 
affects every measurement in the exact same way (which is why it's 
called "systematic"). If you weigh a sample that you know for a fact 
is exactly one pound, then you can correct for the error.

Random errors are harder to spot and harder to correct for. Going back 
to the scale example, it would be as if the scale arbitrarily weighed 
everything placed on it anywhere from a half pound light to a half 
pound heavy. It could even give you the exact right measurement.  
Using the standard weight won't help you this time, though, because 
every time you measure the standard, the scale will read something 
different. Random errors are unavoidable, simply because there aren't 
any perfect instruments, and because people make mistakes. They should 
usually follow a bell curve distribution, though, so you can use 
statistical analyses like standard deviation to try to correct for 
them. You can also try to avoid them as much as possible by using good 
measuring equipment.

I hope that helps. Write back if you have other questions, or if you 
want to talk about this some more.

- Doctor Shawn, The Math Forum
  http://mathforum.org/dr.math/   
    
Associated Topics:
High School Statistics

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