# Multivariate formula with different number of observations

**URL:** <https://discourse.mc-stan.org/t/multivariate-formula-with-different-number-of-observations/16401>\
**Category:** brms\
**Tags:** cognitive-science\
**Created:** [July 5, 2020, 6:02pm UTC](https://discourse.mc-stan.org/t/multivariate-formula-with-different-number-of-observations/16401 "2020-07-05T18:02:28Z")\
**Posts on this page:** 1\
**Showing post:** 19

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**Author:** ![paul.buerkner](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.mc-stan.org/paul.buerkner/32/3303_2.png) [@paul.buerkner](https://discourse.mc-stan.org/u/paul.buerkner)\
**Post date:** [August 4, 2020, 3:41pm UTC](https://discourse.mc-stan.org/t/multivariate-formula-with-different-number-of-observations/16401/19 "2020-08-04T15:41:25Z")

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You can only define a correlation between two variables when there is a one to one correspondence between values. This is not a brms limitation but how correlations work. So i am unsure how you would define this residual correlation in the first place.

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