$($MRH$\_$Ch$01-153)$ Your co$-$worker is looking at archived manufacturing data from the past five years. She says, 'There's a high correlation between purity and our manufacturing yield. In particular, the higher the purity coming in$,$ the better our yields are when we buy from Supplier X$,$ it's our worst results.$\text{'}$

What should your response to this be$?$

Curiosity! Can she look into this data and find any other factors which correlate?

Caution! She has conducted a retrospective study, and did not actually scientifically maninulato nurity