There's an old (and possibly hackneyed) adage that "I know 50% of my advertising works, I just don't know which 50%". In these uncertain times marketers must begin to focus on the 50% that does actually and demonstrably work.

In recession, those companies that continue to market themselves will naturally have an increased share of voice compared with those that do not. As recession draws to an end, when consumer confidence picks up and people start spending money, those brands that have managed to stay front of mind will increase their market share. This is relatively easy if you're Coca Cola (which in the '30s, by spending money in an advertising vacuum – Coke's main rival, Moxie, chose not to – obtained market dominance). But if you're not, then spending money on marketing you can prove works presents a conundrum.

We currently have a confluence of marketing disciplines that provides a solution. Over the last two decades CRM (Customer Relationship Management) has become highly sophisticated. The ability to generate data on customer behaviour, perform detailed segmentation and match it to purchase cycles, has given marketers the means to send precisely targeted messages to increase sales, albeit until recently using direct mail. Separately the digital world has exploded – it all seems so new all of the time. In fact we've now been doing this for fifteen years: enabling consumers to define their interactions with brands and gathering rich learning, whilst putting in place tracking that gives us an unparalleled ability to audit campaigns' immediate effects.

By putting these two disciplines together we have a powerful and accountable means to maintain 'front of mind' contact and directly drive sales. An eCRM programme can be planned in a month, rolled out the following week, and the learning incorporated a week after that. In fact, Dream Team, the world's largest fantasy football league (operated by The Sun) did just that in October. They increased their return on marketing investment (ROMI, or ROI) by 32% in eight weeks.

A properly developed eCRM programme extends beyond customer retention (clearly critical in a downturn) to tactical campaigns, sales promotion, upsell and cross-sell, and brand advertising. Delivering all this online means you can reach specific sets of consumers precisely when you want to (or indeed, when they are most receptive), you can do it fast, cheaply and efficiently. If you have unsold seats on a flight in two days time, you can run a tactical campaign to fill them up. If you see that campaign A beats campaign B by 6%, you can shift from one to the other in an hour. You can check open and click-through rates live, and directly measure brand engagement.

Above all, you can see precisely what works and what does not work and you can spend all of your money on those activities that build revenues. You can, in effect, turn your missing 50% into brand new market share.

Felix Velarde, FreshBusinessThinking.com 6th February 2009