Real benefits of link building campaigns
SEO is an ongoing process, all the technical stuff done, content perfectly optimised so you think link building could be a good next step to improve traffic to a website and the quality of this traffic.
How many times did you have to talk a lot to convince customers to run a link building campaign?
In other words, how can you proof with facts and figures the impact of link acquisition? This is something you have to prove to potential or existing clients, but also to yourself while working on it to review its goodness. Web analytics to the rescue.
The purpose of link building*
- Link building is meant to increase your PR, you say
- So, what? What does it mean?, replies the customer
- Ok, more PR makes the site rank better
- Is this going to bring more traffic and conversions?
- Yes, for sure
- Fine, I want to see the ROI of my precious invested money
*we are talking about natural link acquisition, not buying links.
Campaign conditions
To isolate as much as possible the impact of this link building campaign we wanted no other SEO action to be taken along the time. In the middle of the period, the complete website was changed to make its Xhtml more 'bot friendly' and semantic, so we'll take into account just the first part of it, two months.
Pure referrals segment
Take a look at your referrals panel in your favourite tool, Google Analytics in this case, some of those referrals are not so and we want them not to count in our stats to get more reliable numbers.

1st. Medium: referrals
AND
2nd. Does not match regular expression (mail|search|google|yahoo)*
This way incoming links from email or search engines counting as referral, get out of the game, examples:
images.google.com
mail.google.com
us.mg2.mail.yahoo.com
webmail.aol.com
co106w.col106.mail.live.com
mail.yandex.ru
The difference can be remarkable:

Direct impact
Basically there are two types of links:
1. the ones to increase website relevancy (followed ones + from high PR sites + not reciprocal)
2. the ones bringing traffic (nofollowed ones)
Anyhow, what we see in analytics panel is just traffic coming from links, no matter which type it is, so the first and obvious impact is traffic.

*Change this regular expression (mail|search|google|yahoo) to fit your needs
Indirect impacts
To find interesting answers think about the different ways this could influence key performance indicators and interesting questions will come to you.
Is link building campaign making my keywords perform better? Yes, it is, (remember that while getting new links to your site, one of the best practices is to include some of your main keywords in the anchor text of those new links).
Check the graph and the numbers comparing the link building period and the previous one.

This concept can be applied to conversions or any other KPI, just play around with stats.
Additional data
Links amount
Campaign start: 1
After 2 months: 60
SERP Positions for main keywords
Campaign start: not in first 100
After 2 months: between 11 and 20 (second results page)