Two-lines test

(version 0.52 - beta testing)

Last updated: 2018 11 23 (see how the app has changed over time)

This app runs the u-shape test introduced by Simonsohn (2017 .pdf).
In particular, it estimates an interrupted regression, that is, a regression with two separate slopes, for the predictor hypothesized to have a u-shaped effect. The breakpoint is set using the "Robin Hood" algorithm, seeking to obtain higher power to detect a u-shape if it is present. If the resulting two slopes have opposite sign, and are individually statistically significant, the test rejects the null hypothesis that there is no u-shaped (nor inverted u-shaped) effect.


The output is a chart like this one:

If you know R you may want to:




If you don't know R, or you're feeling lazy. Use this web app

If you don't have a file but want to check things out, download this datafile and then upload it.

Data privacy information.

Uploaded data is deleted within 72 hours. The files are saved, unencrypted, in a public folder but given a temporary name which means it is quite difficult for a third party to find them, but not impossible. For confidential data I recommend downloading the R Code and running locally without uploading the data to the server.




Thanks for using the two-lines test