Hi all,
Last week we discussed our approach to A/B testing and we've decided to have a week (at least) between tests.
A two-week-minimum cadence will give the analysis team enough time to thoroughly think about the experimental design of each test, as well as give the engineers enough time to implement it. Which is great because some of the changes we are planning to test are not trivial and we don't want to rush a test out and realize halfway through that we should have been tracking something we're not.
We are also going to move away from doing initial analyses (analysis of the data from the morning of a launch) for practical and scientific reasons. Practical in the sense that we've been putting time and effort into getting preliminary results that are not representative of final results whatsoever while putting other work on the backburner. Scientific in the sense that peeking at the data mid-experiment is bad science:
*Repeated significance testing always increases the rate of false positives, that is, you’ll think many insignificant results are significant (but not the other way around). The problem will be present if you ever find yourself “peeking” at the data and stopping an experiment that seems to be giving a significant result. The more you peek, the more your significance levels will be off. For example, if you peek at an ongoing experiment ten times, then what you think is 1% significance is actually just 5% significance.* – Evan Miller, How Not To Run An A/B Test http://www.evanmiller.org/how-not-to-run-an-ab-test.html
In science, it's a problem called multiple comparisons. The more tests you perform, the more likely you are to see something where there is nothing. Going forward, we are going to wait until we have collected all the data before analyzing it.
Cheers, Mikhail, Junior Swifty Discovery // The Swifties
On Mon, Aug 31, 2015 at 11:05 AM, Mikhail Popov mpopov@wikimedia.org wrote:
Evan Miller, How Not To Run An A/B Test
If you guys ever want me to get Evan to come talk to us just let know. We both worked at A9 together.
He's a fun guy.
--tomasz
Well, peeking is okay as long as you don't act on it:
“Peeking” at the data is OK as long as you can restrain yourself from
stopping an experiment before it has run its course. I know this goes against something in human nature, so perhaps the best advice is: no peeking!
It does take up time, though, and based only on data from the morning of the deployment it may not give a representative preview. It's still fun to peek, though. ;)
Trey Jones Software Engineer, Discovery Wikimedia Foundation
On Mon, Aug 31, 2015 at 2:05 PM, Mikhail Popov mpopov@wikimedia.org wrote:
Hi all,
Last week we discussed our approach to A/B testing and we've decided to have a week (at least) between tests.
A two-week-minimum cadence will give the analysis team enough time to thoroughly think about the experimental design of each test, as well as give the engineers enough time to implement it. Which is great because some of the changes we are planning to test are not trivial and we don't want to rush a test out and realize halfway through that we should have been tracking something we're not.
We are also going to move away from doing initial analyses (analysis of the data from the morning of a launch) for practical and scientific reasons. Practical in the sense that we've been putting time and effort into getting preliminary results that are not representative of final results whatsoever while putting other work on the backburner. Scientific in the sense that peeking at the data mid-experiment is bad science:
*Repeated significance testing always increases the rate of false positives, that is, you’ll think many insignificant results are significant (but not the other way around). The problem will be present if you ever find yourself “peeking” at the data and stopping an experiment that seems to be giving a significant result. The more you peek, the more your significance levels will be off. For example, if you peek at an ongoing experiment ten times, then what you think is 1% significance is actually just 5% significance.* – Evan Miller, How Not To Run An A/B Test http://www.evanmiller.org/how-not-to-run-an-ab-test.html
In science, it's a problem called multiple comparisons. The more tests you perform, the more likely you are to see something where there is nothing. Going forward, we are going to wait until we have collected all the data before analyzing it.
Cheers, Mikhail, Junior Swifty Discovery // The Swifties
Wikimedia-search mailing list Wikimedia-search@lists.wikimedia.org https://lists.wikimedia.org/mailman/listinfo/wikimedia-search
We will, of course, continue to sanity-check the data within a day or so after a new test starts to run, to make sure that we are logging the information that we will need to perform analyses, that our bucket sizes appear to working as designed, etc.
Kevin Smith Agile Coach, Wikimedia Foundation
On Tue, Sep 1, 2015 at 11:28 AM, Trey Jones tjones@wikimedia.org wrote:
Well, peeking is okay as long as you don't act on it:
“Peeking” at the data is OK as long as you can restrain yourself from
stopping an experiment before it has run its course. I know this goes against something in human nature, so perhaps the best advice is: no peeking!
It does take up time, though, and based only on data from the morning of the deployment it may not give a representative preview. It's still fun to peek, though. ;)
Trey Jones Software Engineer, Discovery Wikimedia Foundation
On Mon, Aug 31, 2015 at 2:05 PM, Mikhail Popov mpopov@wikimedia.org wrote:
Hi all,
Last week we discussed our approach to A/B testing and we've decided to have a week (at least) between tests.
A two-week-minimum cadence will give the analysis team enough time to thoroughly think about the experimental design of each test, as well as give the engineers enough time to implement it. Which is great because some of the changes we are planning to test are not trivial and we don't want to rush a test out and realize halfway through that we should have been tracking something we're not.
We are also going to move away from doing initial analyses (analysis of the data from the morning of a launch) for practical and scientific reasons. Practical in the sense that we've been putting time and effort into getting preliminary results that are not representative of final results whatsoever while putting other work on the backburner. Scientific in the sense that peeking at the data mid-experiment is bad science:
*Repeated significance testing always increases the rate of false positives, that is, you’ll think many insignificant results are significant (but not the other way around). The problem will be present if you ever find yourself “peeking” at the data and stopping an experiment that seems to be giving a significant result. The more you peek, the more your significance levels will be off. For example, if you peek at an ongoing experiment ten times, then what you think is 1% significance is actually just 5% significance.* – Evan Miller, How Not To Run An A/B Test http://www.evanmiller.org/how-not-to-run-an-ab-test.html
In science, it's a problem called multiple comparisons. The more tests you perform, the more likely you are to see something where there is nothing. Going forward, we are going to wait until we have collected all the data before analyzing it.
Cheers, Mikhail, Junior Swifty Discovery // The Swifties
Wikimedia-search mailing list Wikimedia-search@lists.wikimedia.org https://lists.wikimedia.org/mailman/listinfo/wikimedia-search
Wikimedia-search mailing list Wikimedia-search@lists.wikimedia.org https://lists.wikimedia.org/mailman/listinfo/wikimedia-search