Comments on: Stats tip: Within and between subgroup variation clarified http://blog.pqsystems.com/2009/02/03/stat-tip-within-and-between-subgroup-variation-clarified/ Proof of quality. Thu, 09 Feb 2012 14:43:46 +0000 hourly 1 http://wordpress.com/ By: matthewsavage http://blog.pqsystems.com/2009/02/03/stat-tip-within-and-between-subgroup-variation-clarified/#comment-709 Thu, 09 Feb 2012 14:43:46 +0000 http://blog.pqsystems.com/?p=146#comment-709 When you have one subgroup, then you can only calculate the variability “within” the one subgroup. Then you need to decide what are you going to use to represent the variability of the subgroup. Two common choices are the Range of the subgroup (Max value – Min value) and Standard Deviation. Formula is:
SQRT of [(SUM(x – Mean)squared) / (n – 1) where x represents each value in your sample.

]]> By: dewiyenifitri http://blog.pqsystems.com/2009/02/03/stat-tip-within-and-between-subgroup-variation-clarified/#comment-707 Thu, 09 Feb 2012 01:24:51 +0000 http://blog.pqsystems.com/?p=146#comment-707 it is great article,,, but if we have only one subgroup… is standard deviation within and overall same? do you have formula to calculate them? thank you very much

]]> By: matthewsavage http://blog.pqsystems.com/2009/02/03/stat-tip-within-and-between-subgroup-variation-clarified/#comment-691 Fri, 03 Feb 2012 13:25:30 +0000 http://blog.pqsystems.com/?p=146#comment-691 Subgroup standard deviation is typically the variability within the subgroup of X measurement values. X might be 5 if your sample size is 5. i.e. How much variation do you have among the 5 values.

Total standard deviation is the variability with your subgroup AND between your subgroups. This is often referred to the standard deviation of the individual values.

When are they the same? When the variability within your subgroup is the same as the variability as the within and between your subgroups. In short, if your process does not have big swings from start to finish, your total variability will likely be similar to the variability you see within a sample.

]]> By: maria http://blog.pqsystems.com/2009/02/03/stat-tip-within-and-between-subgroup-variation-clarified/#comment-689 Thu, 02 Feb 2012 19:39:44 +0000 http://blog.pqsystems.com/?p=146#comment-689 when are total standard deviation and subgroup standard deviation the same?

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