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Comment by yojo | Hacker News Reader

I don’t know how counting sessions or source of click matters. You still don’t know whether the customer would have ultimately found you without the ad.

Put another way, the only way to tell if a customer will still find you without the ad is to not run the ad.

If you have sufficient traffic you might be able to measure this by turning your ad spend down rather than off and measure the bottom line impact. But other than gross spend changes there’s no way of telling for sure that the ads do anything.

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This is like the paid search results that come up when you search for a specific company name. The company's site is just below those paid results, but often the same site is in the paid results but they are further up so are more likely to be clicked.

> You still don’t know whether the customer would have ultimately found you without the ad.

Sure, maybe 100 customers would eventually find you. But if you buy the traffic, you can make them all find you on the same day.

> But other than gross spend changes there’s no way of telling for sure that the ads do anything.

I'll use the most fundamental example:

If someone clicks your ad and buys the product during that session, you know the ad worked. If you keep increasing your ad budget every day, and you are consistently returning $2 for every $1 you spend, you know it's working. Turn off the ads, and the revenue goes away. You'd be surprised how many people make their living doing this.

> [...] Turn off the ads, and the revenue goes away.

This is the experiment from the article. It showed that ads did not affect revenue.

>If someone clicks your ad and buys the product during that session, you know the ad worked

This is not as clear as you make it seem. Let's say there's a hypothetical product that a consumer only buys once every 5 years. If someone clicks your ad and then immediately buys the product... what if they would have bought it anyway, tomorrow, or 5 minutes from now, without the ad? How can you test that counterfactual?

If I buy cat litter online once a month every month for 5 years by going to example.org/catlitter -- but then they decide to start advertising on facebook, so now I click the facebook ad once a month to buy cat litter from the same site, are the ads "working"?

The idea is because it's happening at scale. If you're getting hundreds or thousands of customers per day, the likelihood of this happening gets lower by some statistical proportion, especially if you don't have the organic exposure.

Also, definition of working: You make more than you spend, and if you stop the ads, you stop making as much.

That said, I'm not arguing for 100% accuracy either. It's certainly not. Simply that it's possible to be more accurate than not, which leads to profitability.

One more also- a comment above about how I failed to mention I'm not talking about paid search ads so much as other types like FB, YouTube, banners, etc.

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