Four Suggestions for Running Experiments More Efficiently

Conducting controlled experiments is the best way of determining whether a site or app redesign would lead to improvements on key metrics. One barrier is the amount of time or resources it takes to run experiments. You may have a low traffic site, you may want to detect small differences in key metrics (i.e. fractions of a percent), or you may want to get experiment results faster. Here are some suggestions on how to run experiments more efficiently.

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Why You Should Combine KPIs in Experiments

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Imagine a company that sells a line of products and services. This company will likely have multiple goals for its website:

  1. to sell its products and services online
  2. to collect user information for sales prospects
  3. to drive brand awareness and loyalty
  4. to provide online support for existing customers

Let’s say the company has identified 20 KPIs (Key Performance Indicators) that measure the success of these four goals, and it is committed to optimizing the conversion of these goals by running many experiments. Should the company launch the treatment if some KPIs perform better but others perform worse than the control (i.e. the original site)?

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Google Statisticians: Looking Beyond P-Values

There’s a recent term called “Google Statisticians.” No, they are not statisticians who work for Google; they are people who do statistical analyses by googling words like “how to do significance testing” or “how to calculate p.”

As biostatistician Jeff Leek pointed out, most analyses are no longer performed by statisticians, as data are now abundant and cheap to collect. Long gone are the days of door-to-door surveys, and phone surveys are almost a thing of the past. Online surveys are everywhere due to platforms like Lime Surveys and the powerful Google Consumer Surveys that make it easy to collect and analyze survey data. Log file data is free and overwhelming in size. There’s even software geared towards non-statisticians that automates statistical analyses.

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What if my sample size is not big enough for my experiment?

My main recommendation – include only users impacted by the change in your analysis; exclude users who are not.

  • Let’s say you have an e-commerce site. You want to test whether certain changes to your checkout page would increase conversion (% of users purchasing).
  • You want to run a 2 x 2 Multi-Variable experiment with 1 control and 3 treatment groups.
  • Your current conversion is 5%; you want to detect conversion changes as small as 10% (with the conventional 80% probability of detection and confidence level at 95%).
  • According to this table in my blog post, you would need 30,400 users in each group, or 30400 x 4 = 121,600 users in total visiting your site. (That’s a lot!)

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3 Steps to Calculate Sample Sizes for Experiments

To calculate how many people you need in your experiment, you need to know 3 things:

1. How many groups are in your experiment?

  • In an A/B experiment with a control and treatment group, you have 2 groups.
  • In a 2 x 2 Multi-Variable experiment with 1 control and 3 treatment groups, you have 4 groups.
  • The more groups you have, the more people you need.
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