The only way to really test it is to measure the outcome of those messages.
Eg is there a way to correlate the number of tweets to the number of new downloads.
Speaking purely about twitter, the easiest way to measure virality is to see how often a tweet gets retweeted.
For example, I have a website whendidyoujointwitter.com - it has a 'tweet this' type of link. Often when someone tweets that link, some of their followers will go the link in their tweet and in turn tweet their own message. We can then measure the virality if we see on average how many followers do this 'retweet'.
Eg if someone with 1000 followers tweets it and then 10 of their followers tweet it as well, this is a success rate of 1%.
Now, this is still not a virality percentage. We have to go a step further by asking how many followers does the average twitter user have? If everyone had 1000 followers, then those 10 retweets would result in 100 retweets which would result in 1000, etc (until it peters out - there are only so many twitter users/people in the world) - ie very viral by most standards.
BUT not all twitter users have 1000 followers. What we can try to calculate is a tipping point. With a success rate of 1%, how many followers would the average user need to have in order for the meme to keep spreading?
If the average is 100, then 1% means a tweet would result in 1 more tweet - ie the meme would be kept alive. If the average is less than that, then the meme is sure to die out.
Now, going in reverse, the latest stats I can find show the average follower count is 70. So a success rate of 1% is not enough to go viral - it would need to be up around 2% or above.
Uhhhhm so thinking about, I guess it's a logarithmic/exponential thing.
- 100% success rate (all retweet) =
- 10-99% = extremely
viral through this whole range
- 2% success rate = viral minimum
- 1% or less = not viral