How to tell if a billboard worked

A billboard worked if something you care about moved, in the place and the time you'd expect, and nothing else explains it. You can check that without a research budget.

Most outdoor campaigns end with a report of impressions. That tells you how many people could have seen the board. It doesn't tell you whether anyone did something because of it. Here is the method we use, in the order we use it.

1Pick the one number first

Decide, before the booking is signed, what you want to move. Choose one. Good candidates are searches for your brand name, visits to a specific page, calls or WhatsApp enquiries, store visits, or sales of one product.

If you decide after the campaign, you'll find something that went up and call it a result. That isn't measurement. It's picking the winner after the race.

2Set a baseline

Write down that number for the four weeks before the campaign starts. Note any weekly rhythm, such as weekends or payday. Without a baseline, "traffic went up" has nothing to compare against.

The comparison you choose should be stated up front. The results on our home page use three different ones: against the previous month, over six months, and year on year. Each was agreed with the client before we looked.

3Look where the board is

A board in Bukit Bintang should be felt first by people in and around Bukit Bintang. If you can split your numbers by area, compare the neighbourhood against one that never saw the board. If the whole country moves equally, your board probably isn't the reason.

• Brand searches: people who see a board often search for the name later. Look at the trend in the weeks it ran.
• Direct and mobile traffic: visits by people typing the address or arriving on a phone.
• Enquiries: ask every new customer where they heard of you, and write down the answer.

4Rule out the other causes

Write down everything else that changed in the same weeks: a promotion, a social campaign, a festival, a price change, a competitor's news. You won't remove these, but you can show them next to the result so nobody is misled.

If you can't say what else happened, you can't say what the board did.

5Report it honestly

Put the number, the baseline, the dates and the caveats on one page. If the lift is small, say so. A campaign that moved the number a little, at a low cost, can still be the right buy. A campaign that moved nothing is useful too, because it tells you where not to spend next time.

Before your next booking

• One number chosen and written down
• Four weeks of baseline recorded
• Comparison period agreed in advance
• A place to split the data by area
• A list of other things running in the same weeks

This won't give you a laboratory result. It will give you something better than impressions: a number you can defend in a meeting and use to plan the next buy.