Some help with the viral loop

by Kristofer Mencák on October 4, 2010

First of all, I don’t like to use the word “viral” about something that hasn’t proven itself viral yet, but many people use it anyway. To them, it is simply the easiest way to refer to an upcoming campaign they hope will become viral.

Whether or not it actually becomes viral, it is well worth the time to think about how that hoped for virality will be achieved. In short, the basic reproductive number (or rate) needs to be above 1 for the campaign to become viral. And, if we simplify it a bit, the two variables making up R are (I have chosen X and Y in this case) are:

X = The ratio of receivers of the campaign who pass it on
Y = The average number of people someone who passes it on, sends it to

The first one, X, is between 0 and 1, with 1 representing 0 % and 100 % of receivers. The second, Y, could be between 1 up to (theoretically) infinity.

So, X * Y = R

What does this tell us? Well, X * Y needs to have a product above 1 to go viral. Since X can be, at most, 1, Y needs to be above 1. Some examples:

If X is 50 %, Y needs to be more than 2 to become viral (0,5*2=1)
If X is 25 %, Y needs to be more than 4 to become viral (0,25*4=1)
If X is 10 %, Y needs to be more than 10 to become viral (0,1*10=1)

It happens that I get to review campaign suggestions where the supposedly viral loop is built up to have a Y of 1. This can never go viral. It is not realistic that 100 % of people exposed to the campaign will pass it on, and even if they did, with Y=1, the basic reproductive number would never be above 1 and it can’t take off exponentially.

So, when trying to build in a viral loop, think about the two factors that will affect the basic reproductive number.

If you want to learn more about viral marketing and contagious messages, here is a tip for a book I really like.


Kristofer Mencák is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com.

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