The ROI Model that Tamar Weinberg describes in her book, The New Community Rules, describes 5 categories of metrics used to determine Social Media return-on-investment.

The model describes five measuring categories, which are defined by different measuring elements.

Reach
How far does your message reach? Elements are: links generated through messages, tweets about messages, quantity of people talking about your message and acquired new connections by generating valuable content.

Frequency & Traffic
These are factos that can be described as ‘quantity factors’, like: visits, unique visitors and returning visitors.

Influence
What is the reach of a conversation once started? And to what influence? Elements include: discussions about a message or content, related comments, retweets and quantity of sharing and sending the message.

Conversation & Transaction
What is the call-to-action and is it working? Elements in this section include: frequency of click-throughs to your website, downloads and sales.

Sustainability
Is it just a single visitor, a returning visitor or is it a loyal ambassador that is embracing your content? Elements are: sustainability of community members, loyalty and frequency of returning visits.

Source: The New Community Rules – Tamar Weinberg