I’m just finishing a run but it appears that you are correct! Thank you so much for your help. Out of interest could you help me understand why sampling mean[:, product_data] fails? The reason for my confusion is this is similar to the syntax used to slice tensors in tensorflow. For PYMC are tensors held a little differently? my intuition would be we have a tensor generated here for each input, so we need to take the respective tensors then select the product value internally from that tensor, is that anywhere near reality?