The mean age of participants in your study is 20.1 years with a standard deviation of 2.7 years. As you write up your results, y
ou realize that what matters is the ages of the participants two years ago when the event happened, not their ages now. You decide to subtract 2 from each of your participants’ ages. After you subtract 2 years, the mean age in your sample is18.1 years. The new standard deviation of the ages in your sample is________ years.
When equal value is added or subtracted from each data item, the mean changes by such a value. However, the standard deviation does not change. The standard deviation measures how far the data items are from the mean. Because the mean has been changed by equal amount as the data items, the average "distance" of the data item from the mean does not change.
Of note is that the standard deviation would change if each item was multiplied by the same factor. In that case, the standard deviation would be multiplied by the same factor as well as the mean.
