The Inspection Paradox

The Inspection Paradox

Many are aware of the so-called friendship paradox of social networks, which was mentioned in one of the investigations in 1991 when social networks were offline. However, this paradox can be applied to modern online networks as well. This is actually a type of the famous inspection paradox.


The friendship paradox consists in the following: if we take any Facebook user and choose randomly any of his/her friends, we will find out with 80% possibility that the latter has more friends than the former.

In fact, there is nothing unusual. The essence of this paradox is that users who have more friends become a statistical sample more frequently. According to Stanford Large Network Dataset Collection an average Fb user out of 4000 users has 42 friends, but each friend out of these 42 has an average of 91 friends.

One may come across the inspection paradox quite often and it may even lead to delusions and mistakes. Here is a famous example: university students selected randomly are asked about the size of their group and according to their answers the arithmetic average is 56 people, though the university administration says there are only 31 students in each group on average. Surprisingly enough, but both the administration and students tell the truth. The thing is that people from larger groups have more chances to become a statistical sample just because there are more of them.

This mistake may seem quite trivial, but it is a reason for misunderstanding in many situations. The American professor of Mathematics Allen Downey provides an example of such a mistake. He observed the Red Line trains in Boston between 17:00 and 18:00 and arrived at a conclusion that the average interval between trains was 7.8 min. So, the average waiting time must have been about 3.9 min, but according to passengers the average waiting time was 4.4 min and the average interval between trains – 8.8 min. Thus, the difference was almost 15%.

The explanation is more than simple. During longer intervals, there are more people crowding on the platform and awaiting the next train, while during shorter intervals platforms and trains are less crowded. Obviously, there are more possibilities to select as a sample those people who are waiting during a longer period. The result is as follows: the majority of interviewed people complained about overcrowded trains and long interarrival time, whereas the company officials said that according to their data everything was within normal range.

And what do YOU think about it? Have you ever happened to come across this paradox?

#Science

Your opinion matters
10 Comments
Thomas Bachwitz
Thomas Bachwitz
Look, I'm confused to begin with-in the words of James Dean..."You're tearing me apart !".
0
Sep 15, 2015 9:34PM
Annette McConnell
Annette McConnell
what did you just write ?!? And who cares? not interesting not even comprehensible. I'm disappointed in you guys.
1
Sep 15, 2015 10:17PM
Jeanne Reyes
Jeanne Reyes
Lol. It does make sense, but not an easy concept to grasp. The example from the train is easier to understand than the former two, though.
1
Sep 15, 2015 10:27PM
Jim Wilson
Jim Wilson
sounds like a pyramid scheme ,LOL
0
Sep 15, 2015 11:59PM
Judy Bartel
Judy Bartel
Ditto Annette, who cares
0
Sep 16, 2015 12:01AM
Ian Millman
As Einstein said, if you can't explain it clearly and simply, then you haven't understood.
5
Sep 16, 2015 1:10AM
Malella Valentekovich
Malella Valentekovich
statistics sometimes can work for you advantage, depending how you calculate them.
0
Sep 16, 2015 2:05AM
Sarah Hearn-vonFoerster
Sarah Hearn-vonFoerster
Any study of statistics is mind-boggling....and Efficiency Gurus(Corporate Nazis) DO care.
0
Sep 16, 2015 4:50PM
Vasily Tchaikovsky
Vasily Tchaikovsky
good soviet saying:only friends can betray. I follow this and OK
0
Sep 16, 2015 6:21PM
Glyn Pollard
Gosh! I had such a crush on James Dean 💓💓
0
Nov 21, 2017 1:26PM

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