BBC College of Journalism Blog - A vigorous and robust discussion about journalism from every perspective.

Twitter sophisticates wouldn't be caught dead admitting they're interested in how many Followers they have. No, it's all about influence - not the quantity but the quality of your Followers.

To help you measure influence, tools like Klout and PeerIndex crunch numbers for your account, scoring things like how much your tweets are noticed by people who are well connected with other important people (a bit like how Google ranks the importance of a web page by the pages it links to).

But there may be the start of a backlash against these complex systems (see Aleks Krotoski in last month's Wired). And it seems to me they have led to the simple numbers that Twitter makes freely available being under-used.

For journalists, how many people you reach must be of interest. And while Follower numbers are by no means a definitive measure of that (because retweets multiply the reach of a tweet), they do surely give some index of the impact and recognition of the tweeter?

The Independent recently came up with a Top 100 UK tweeters based on PeerIndex measures of activity, audience engagement and authority ('using an algorithm called "eigenvector centrality"' - phew!) mixed with some subjective judgment by its expert panel.

Here, I've gone back to basics to look at numbers for some of those top accounts, using three metrics: Followers, total number of tweets and days since joining Twitter (which I got through twbirthday).

Where The Independent used its panel's judgment, the subjectivity here is in the picking of my sample: I just went for 20 top names - ten journalists and ten celebs. So the following is not claiming to be anything more than an exercise in trying out some simple Twitter metrics.

First, how many Followers do members of my group get for each tweet they send? This 'how much bang for your buck?' test is simply numbers of Followers divided by numbers of tweets.

First, the celebs: 

Richard Branson - Britain's top tweeter according to The Independent - comes only sixth of these ten in terms of number of Followers. But because he has tweeted relatively little (just over 1,000 tweets compared to Jonathan Ross' 17,000), in terms of building his audience his tweeting is much, much more efficient than for those at the bottom of this chart.

But even at the bottom of this list, where Richard Bacon is getting 98 Followers every time he tweets, that's much more than anyone on my journalist list. Top here (below) are Alan Rusbridger and Robert Peston, with around 34 new Followers for every tweet.

India Knight is in a class of her own with only about one Follower added for every tweet (next up is Channel 4's Faisal Islam with three). That's because of Knight's extraordinary output: a total of 51,000 tweets, an average of 45 per day (if you Follow, this is the kind of gory detail you can expect). The only person coming close to Knight for sheer output is Caitlin Moran, with 43,000 tweets. But, because she has more than three times as many Followers, she's still on about five Followers per tweet.

There are plenty of possible objections to drawing conclusions from these figures - that celebs acquire Followers by name recognition alone, for instance. But, when a journalist is being paid to put time into tweeting, a crude measure of how efficiently he or she is building an audience must be of interest. Even for celebs, whose audience may be more easily acquired, this measure still indicates whether tweets are welcome: Unfollow is always only a click away.

Using 'when joined Twitter' figures, I also looked at how fast these accounts have been building their audience. A million Followers is more impressive if you've only been on Twitter for three months rather than for three years.

So here I've done another simple sum: number of Followers divided by number of days on Twitter:

Gary Barlow's runaway lead is due to his only having been on Twitter since October, whereas Richard Branson joined in 2007.

Here's the journalists' equivalent:

If it's good - with all the caveats - to gain more Followers per day, and more Followers per tweet, we can add those two figures together to produce (drum roll) an exciting new Twitter Potency Index (TPI) - unveiled here for the first time.

Below, I've ranked my TPI scores for this sample. Once again, celebs outpace journalists, with the lowest celeb score (Richard Bacon) way ahead of the top journalist (Hilary Alexander).

Among the celebs, Gary Barlow, being a Twitter new boy, and Rio Ferdinand, the third-most recent joiner (after Lord Sugar), both get a boost through high Followers-per-day scores. But Stephen Fry is still up there after almost four years on Twitter thanks to his high Follower number (almost 4 million, the most of these ten) and modest daily activity (eight tweets average, only the seventh-most frequent of these ten celebs), making his tweeting more effective in adding Follower numbers.

Of course, my TPI measure isn't perfect: for instance, it would penalise someone who set up an account and then didn't use it for six months (depressing their Followers per day measure). But, as a crude measure of Twitter dynamism, or whether it's worth the tweeter spending their valuable time on it, I think it says something. The huge range, even within this group, indicates massive differences, I'd argue, in the basic efficiency with which Twitter is being used. And these are all Twitter stars: less impressive numbers for others might suggest the need for a rethink.

To check your own Twitter potency, use this formula:

Total Followers/Total tweets + Total Followers/Age of account (in days) = TPI

To get within range of this group of pros, you're aiming for Faisal Islam's score of 33.

In a follow-up blog I'll look at whether there's an optimum rate of tweeting, and how the Twitter efficiency of journalists and celebs compares to that of public bodies and big companies.