When we say a statistic is resistant, we mean the extreme values do not affect the statistic to a large extent or to an extent which makes a major difference. Mean and median are example of such statistics. By changing the extreme values we do not see a substantial difference in the value of mean and median for the data set.
Consider a sample: 1,2,3,4,4,5,6,7,8 The median for this data set is 4. If we change the extreme values to get this sample: -5,2,3,4,4,5,6,7,100 The median will still be the same i.e. 4. This is what is meant by a resistant statistic.
It doesnt mean they are false it just means the person giving the study is going to favor something over something else in the study. Hes basically picking favorites.
