Please, if you are teaching an overview of electoral system effects, consider using this. It is much more lawlike in its scientific derivation and empirically accurate than the (in)famous "law" that too often gets taken as if it were literal binding law. https://twitter.com/laderafrutal/status/1300857872595718144
Let me add: the heavy intellectual lifting in developing the seat product model was borne by Taagepera. He won the Skytte Prize, basically our Nobel, in 2008 for "his profound analysis of the function of electoral systems in representative democracy."

https://www.skytteprize.com/#prize-winners 
For the longer-form version of the seat product model, refer to our 2017 book. For a medium-form version, we have a chapter in the Oxford Handbook: https://twitter.com/laderafrutal/status/984608176099147776
First hint of what became Seat Product Model was in our joint APSR paper, 1993. But we referred to it as "SM"; for various reasons, I much prefer calling it "MS"!

(First place it was fully presented would be Taagepera's 2007 book, Predicting Party Sizes.)
https://www.jstor.org/stable/2939053?seq=1#metadata_info_tab_contents
And to go direct to the datasets (one nationwide, the other district-level):

https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/ME2W6U
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