Monday, 1 December 2014

Why do you read A/B testing case studies?

Case studies.  Every testing tool provider has them - in fact, most sales people have them - let's not limit this to just online optimisation.  Any good sales team will harness the power of persuasion of a good case study:  "Look at what our customers achieved by using our product."  Whether it's skin care products, shampoo, new computer hardware, or whatever it may be.  But for some reason, the online testing community really, really seems to enthuse about case studies in a way I've not seen anywhere else.


Salesmen will show you the amazing 197% uplift that their customers achieved through their products (and don't get me started on that one again).  But what do we do with them when we've read them?  Browsing through my Twitter feed earlier today, I noticed that Qualaroo have shared a link from a group who have decided that they will stop following A/B testing case studies:

And here's the link they refer to.

Quoting the headlines from that site, there are five problems with A/B testing case studies:

  1. What may work for one brand may not work for another.
  2. The quality of the tests varies.
  3. The impact is not necessarily sustainable over time.
  4. False assumptions and misinterpretation of result.
  5. Success bias: The experiments that do not work well usually do not get published.
I've read the article, and it leaves me with one question:  So, why do you read A/B testing case studies?  The article points out many of the issues (some of them methodical, some statistical) with A/B testing, leading with the well-known 'what may work for one brand may not work for another' (or "your mileage may vary").  I've covered this, and some of the other issues listed here before, discussing why I'm an A/B power-tool skeptic.

I came to the worrying suspicion that people (and maybe Qualaroo) read A/B testing case studies, and then implement the featured test win on their own site with no further thought.  No thought about if the test win applies to their customers and their website, or even if the test was valid.  Maybe it's just me (and it really could be just me), but when I read A/B testing case studies, I don't immediately think, 'Let's implement that on our site'.  My first thought is, 'Shall we test that on our site too?'.

And yes, there is success bias.  That's the whole point of case studies, isn't it?  "Look at the potential you could achieve with our testing tool," is significantly more compelling than, "Use our testing tool and see if you can get flat results after eight weeks' of development and testing".  I expect to see eye-grabbing headlines, and I anticipate having to trawl through the blurb and the sales copy to get to the test design, the screenshots and possibly some mention of actual results.

So let's stick with A/B tests.  Let's not be blind to the possibility that our competitors' sites run differently from ours, attract different customers and have different opportunities to improve.  Read the case studies, be skeptical, or discerning, and if the test design seems interesting, construct your own test on your own site that will satisfy your own criteria for calling a win - and keep on optimising.

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