Explaining PCA to a school child

Ed Yong asked on Twitter “Explain principal component analysis to a schoolchild in a tweet.” Since I can’t explain PCA eloquently, I found this interesting and wanted to keep a record of the replies for future reference. Here are some of the modified replies, with my favourite first (and the rest in no particular order):...

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Step by step principal components analysis using R

I've always wondered about the calculations behind a principal components analysis (PCA). An extremely useful tutorial explains the key concepts and runs through the analysis. Here I use R to calculate each step of a PCA in hopes of better understanding the analysis. I'm still trying to figure out why the signs are inverted between...

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