For my chemistry class, I have to do some statistics on a set of data. One of the things I have to do is eliminate outliers via the 4D rule. Unfortunately my teacher is also absent, so I can't get this question answered.
The 4D rule goes like this on my stat sheet:
Calculate mean and standard deviation.
Establish a range of acceptable results by adding and subtracting two standard deviation units to/from the mean.
Calculate new mean and standard deviation after excluding the results that are out of range.
Multiply new standard deviation by four and calculate the difference between each of the original results (without exclusions) and the new mean.
If the differences calculated is greater than 4 * standard deviation (calculated in step 4), it is valid to exclude the trial.
And my data points are: 1.1, 4.5, 9.4, 9.7, 9.9, 10.2, 22.2. (they are rounded short for this post)
Mean: 9.6, standard deviation: 5.3
Is it correct to then say that the acceptable range is -1 to 20.2. So I can only exclude the last data point and not the first two?
Would the results be difference if I changed the measurements from micrometers to nanometers then?