Does adding data to a data set affect the standard deviation?

[JaredNardi]

Hi, quite a basic question here but I can't find a solid answer.
If I had a data set of 10 points, and I chose to add 4 new data points to it for example, can I use the same original standard deviation? Or must I re-calculate it? Is it possible to add the new data points with a specific number in which the standard deviation will stay the same as originally?
Thanks!

 

[IslaDuffy]

You definitely need to recalculate. We wrote a case study for a similar task. Because you added 40% new data, which may well affect the end result. Your case study data can provide two different answers.

 

[hlsmith]

Agreed, as @IslaDuffy stated a recalculation is necessary. Think about the formula components, mean, n-value, obs, they have all changed.