# Using DifffEqBayes.jl for fitting y(x) instead of time series

**URL:** <https://discourse.julialang.org/t/using-difffeqbayes-jl-for-fitting-y-x-instead-of-time-series/99026>\
**Category:** Statistics\
**Created:** [May 17, 2023, 11:32pm UTC](https://discourse.julialang.org/t/using-difffeqbayes-jl-for-fitting-y-x-instead-of-time-series/99026 "2023-05-17T23:32:09Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![PeX](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pex/32/49986_2.png) [@PeX](https://discourse.julialang.org/u/PeX)\
**Post date:** [May 17, 2023, 11:32pm UTC](https://discourse.julialang.org/t/using-difffeqbayes-jl-for-fitting-y-x-instead-of-time-series/99026/1 "2023-05-17T23:32:09Z")

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I was wondering if there is an option in DiffEqBayes.jl or another package to make MCMC parameter estimation that fits one of the variables as a function of the other, rather than the time series of each.  
Let’s say I have a system that looks like this:

dx/dt = αx - βx  
dy/dt = γx + ηy

But my observational dataset is y(x). Is there a way to use it for the parameter estimation of the ODE? (I know it’s unintuitive since there is an underlying assumption that y and x are independent, however, this is the only type of data I have)