Very interesting stuff!  
I haven't actually got around to doing a Bio. I'm off to do one now though and I'll be watching to see if my new followers increases.

I was just twittering about this very thing yesterday. Bio and link are a must. Good article.

Thanks for sharing this proof. 
 
I usually do the same when following a new person. It is b'coz I can't know the exact name on twitter and I want to know who are those people I'm following. Sometimes it helps me to give them reply. 
 
And a good trick to let people follow you is to comment on their posts or their website/profile as soon as you want to follow them. I experimented this and found it 100% successful where I use it. When I don't use this the success rate is just 10%. This way you can be in better contact with people 
 
Thanks

Users that have a link and a bio lets someone know if it’s a real person and not spam. No one wants to follow someone if it’s just spam.

Dan, 
 
Interesting post, thanks for sharing. I definitely check someone's bio typically before following. 
 
However, I would argue that the real reason for the correlation here is because people w/o bios are new and inexperienced or inactive twitterers who aren't really following many people yet.  
 
They don't have a bio, b/c they're still getting adjusted to the medium, and they don't have many followers because they haven't tweeted much yet or followed others. That's the reason for their low numbers not strictly because people don't follow those without bios. 
 
Maybe run a report on # following for each demo, and I'll bet you see a similar, if not greater ratio as in the post.

I would be curious about the # of followers for different types of links in one's profile: website home page, blog, specific landing page for Twitter users or something else. Or does it make a difference?

Kinda common sense for anyone who uses Twitter more than a little bit. But, it's certainly interesting to see the data nonetheless.

maybe they havn't posted a bio or link because no one is following them.

I find that I always look at the person’s bio and link. If they don't have one, I rarely follow that person. I think the same holds true for most all of social media. If I can’t get even a little information about you, then why would I, fill in the blank (follow, link, connect, friend…) you? A certain level of transparency is key, just like in a face to face networking environment or simply meeting someone for the first time.

Great article, i have been convinced to join twitter this week and have been looking for good information before i go ahead. 
 
thank you

I tend to agree with Clay: there is no proof that there exists a correlation "if you have a Bio you will get more followers". The correlation could be exactly the opposite ("the more followers you have the more interesting it would be to have a bio"). 
Or, as Clay states, there could be a third variable linking both (usage of Twitter; the more you use it, higher chances you have a bio and more followers)

I suppose having a bio does not necessarily cause you to have more followers but it seems to make a lot of sense to have one anyway based on this data and the comments here. I certainly have no interest following people w/o a bio and link. Now if I could only figure out how to write a GOOD bio....

looks like self selection...

I tend to look at the bio when I choose whether to follow a person or not but the most important thing that I care about is their tweets. Good job on publishing the stats on this and I hope that people who are new on Twitter will have an interesting bio to increase their follower count instead of using some spammy scripts.

Clay hit it on the mark - there is a correlation between bio/link and level of engagement. A casual or cautious commitment to Twitter is reflected in a reluctance to offer up personal information such as a bio or a link. It's all about engagement, baby.

This makes perfect sense. I wouldn't respond to an email if the sender wasn't clear on who they were or their intentions for sending the email in the first place. 
 
 
 
I view Twitter in the same manner. If someone does not have a bio, I don't feel as though they are validating their intentions on Twitter. Are they spammers, are they just following for the sake of following, etc.? 
 
 
 
And especially on Twitter, there is no reason not to fill our a bio. It's only 140 characters worth of explanation! Bios and links show to the Twiterverse that you are, infact, a real person with a genuine desire to make connections.

I was wondering about the question Clay posted as well, on other reasons casual users may not have many followers.  
 
 
 
However, I really value having a bio to look at when I'm considering whether to follow someone, as not everyone uses their full or real name in their profile. 
 
I'm off to create my own right now! Hello!

Wow!!! Never realised the importance of this. Just updated my twitter profile pronto. Thank you for a great site. Just recommended it on my blog.