Here’s a quick question: what is the most important number for your union’s Facebook page, Twitter account or website?

Take a few moments to consider the answer before you read on.

If my experiences with a number of unions and non-profits is representative, I’m willing to bet that “traffic” or “page views” or “likes” or “followers” was your answer. These are all effectively the same thing.

The reason that you want followers, fans or lots of visitors to your union’s website is acquisition. This could be supporter acquisition, through people signing petitions, member acquisition through people joining your union online, or donor acquisition if your union is fundraising for a specific reason (or even customer acquisition if your union sells merchandise).

Almost every union is focused on acquisition off-line. Union growth is about acquiring new members. Organisers, call-centres and delegates all work to get new members.

Online and with social media, there is (or should be) the same focus: getting new supporters and members.

The focus on acquisition is pervasive.

Here’s the thing. This focus, especially online, is back to front.

The obsession of every union official and elected official concerned with social media and digital campaigning should be on conversion.

Conversion is all about how to turn your audience into supporters, members, donors, delegates, or activists, most efficiently and effectively.

In social media and digital campaigning, the key to conversion is optimisation: the art and science of making small changes to the design, text and messages on your website and social media accounts to increase the number of people who “convert” from audience member to member/activist/supporter.

Basic conversion is easy to understand and calculate.

Simply put, conversion is the ratio of visitors/fans/followers that perform a desired action, divided by the total number of visitors/fans/followers.

Your website or Facebook page likely has a single overall conversion rate. Your website using Google Analytics likely has a conversion rate. Your Facebook page Insights will have a “post clicks” number.

To really master conversion, you need to realise that conversion is determined not at a site level or Facebook page level, but each individual page or post, and for each campaign.

Because of the rapid rise of mobile, you will also want to know your conversion for mobile and tablets as well. It will likely be different from desktop ratios.

The reason that conversion is so important is that you can make small improvements to your conversion rate that can result in significant improvements to your digital campaign results. The improvements come because you turn an audience you already have into members or supporters, rather than needing to spend time and money finding a new audience.

The gains in conversion improvement are best when dealing with large numbers, for example union public advocacy campaigns during election periods. But the benefits still exist for union digital or social campaigns dealing with 10s or 100s, rather than 1000s of potential supporters or members.

Unions already know this intuitively when dealing with face-to-face organising and recruiting. There are two kinds of growth organising, one focusing on quantity of “asks” to join, and the other focusing on the quality of asks.

The basic maths of the first “quantity” means that if you ask 100 people to join your union, you’ll get two or three to join. Unions that focus on bulk asks, blitz and the like have an acquisition approach.

The “quality” side means improving your script, training your growth organisers, sending them to primed areas rather than cold sites. This could mean you only need to ask 50 people to get three people to join the union.Your conversion rate is twice as good, so you halve the time and resources needed to get the members. So long as the investment in training, and priming doesn’t double the cost of recruiting a new member, you’re ahead. This is a conversion approach.

The analogy is buying fuel for a car. Most organisations focus on buying lots of fuel in the hope of getting bulk discounts (this is new member acquisition). Instead, you should be focusing on getting your car running as efficiently as possible, so you don’t waste a single drop. Once you’ve done that, start buying bulk fuel.

Because unions are starting to increase their digital and social media spend, especially on things like promoted Facebook posts or other online ads, it’s essential that your website be able to effectively and efficiently convert your potential supporters, which you’ve paid money to send to your campaign website.

In practice, for social and digital campaigning, there are scores of little things you can do to improve your conversion rates. The challenge is that the changes you need to make are probably not immediately obvious to you.

Even the much vaunted Obama digital team couldn’t intuit what would work.

Writers, analysts, and managers routinely bet on which lines would perform best and worst. “We were so bad at predicting what would win that it only reinforced the need to constantly keep testing,” says Showalter.

If the experienced operatives in Obama for America couldn’t guess what kinds of email subject lines or landing page images would work most effectively, do you really think you can do better?

What they did, and what more and more unions are starting to do, is invest in digital testing. This especially means A/B testing for things like email subject lines, but it also increasingly means testing your website.

While lots of unions are spending time, energy and money on social media campaigning (and this is good although avoid vanity metrics in social media), it is far, far more important to invest time beforehand on optimising your campaign website.

The topic of conversion optimisation for campaign websites receives repeated mention in my Guide to Online Campaigning for Unions.