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+What denominator to use for relative vote shares?
+
+Since 1970s, PRI was the obvious choice. Was the hegemon. And convenient methodologically as it was never zero.
+
+Morena's takeover has shaken that. Since 2018, the PRI began teaming up with its former main oppositions. Zero became frequent overnight.
+
+2024 will show if Morena should become the new denominator. This methodological shift complicates temporal comparison. Reminiscent of APD's party system changes in US historical studies. Fifth party system, Sixth, and so forth.
+
+Check Burnham and APD to view how they deal with before/after comparisons. UCSD library.
+
+Check Molinar's identification of Mexican post 1917 party systems.
+
+|                                         |             | Obvious     |
+| Party system                            | Period      | denominator |
+|-----------------------------------------+-------------+-------------|
+| 0. (Prerrevolución, otro proyecto)      |             |             |
+| 1. Post-Convention pluralism            | 1920s       | no          |
+| 2. PNR skyrockets                       | 1930s 1940s | PRI         |
+| 3. PAN and hegemonic zenith             | 1950s 1960s | PRI         |
+| 4. Olympic crisis and the excluded left | 1960s 1970s | PRI         |
+| 5. LFOPPE PRI's meltdown                | 1980s 1990s | PRI         |
+| 6. IFE Triumvirate/Partidocracia        | 2000s 2010s | PRI         |
+| 7. MORENA's takeover                    | 2020s       | MORENA      |
+
+
+