Summary statistics, whether mean, standard deviation or any other single
number, are useful, but sometimes they can mislead - vastly different data
sets can have similar or even identical summary statistics. In the video
below Robert Kosara discusses this
phenomenon in more detail.
Thus here we give you an opposite advice to the one we gave
previously. You should plot the data
to see whether summary statistic you have obtained make sense.
Well, you should actually always do both things - visualize the data and do
some tests or summarization. If intuition from the visuals and the numbers
differs, then you should look for things that may have gone wrong.