Sigma
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Most have heard of the "bell curve" in mathematics. This is the shape that describes the probability that a given percentage of measurements will fall in the region under the bell curve. Gausian Distribution simplified means that if you measure the same thing many times and make a vertical bar for each measurement value you can get, the bar graph will have a bell shape centered around the actual measurement. The width compared to the height of the bell shaped graph can be described with a statistical measurement called standard deviation or sigma. Basically, this is a measurement of how much the measurements vary around the actual value. Now three sigma is 3* the standard deviation, which statistically mean that 99.73% of the time a measurement is made it will be within 3*the standard deviation of the actual value. It is thus a way to compare how good the measurement method is. In similar ways 2 sigma means within 95% of the actual value and 6 sigma means as close to always as is resonable to ever need. |
