The following was a comment by Manuel on a post about the 2018 election. It certainly deserves a more prominent planting hole, so I am copying it here. Please note the following is authored by Manuel Alvarez-Rivera of the always valuable Election Resources on the Internet, not by me.
Note Manuel’s very interesting observation that this time the system functioned as pure mixed-member majoritarian (MMM), i.e., with “parallel” allocation of the single-seat district and list components, rather than with any compensatory allocation.
Preliminary results of the June 6, 2021 Chamber of Deputies election in Mexico indicate that no gaming of the 8% disparity cap took place this year, largely because the ruling “Juntos Hacemos Historia” (JHH; Together We Make History) coalition won fewer single-member mandates than in 2018.
With 99.6% of the tally sheets processed, Mexico’s Preliminary Election Results Program (PREP) reports the distribution of Chamber of Deputies single-member seats stands as follows:
PAN – 33
PRI – 11
PRD – 0
PVEM – 1
PT – 0
MC – 7
MORENA – 64
PES – 0
RSP – 0
FXM – 0
PAN-PRI-PRD – 65
PVEM-PT-MORENA – 119
The PAN-PRI-PRD “Va por México” (VPM) opposition coalition ran candidates in 219 of 300 Chamber districts, while JHH (PVEM-PT-MORENA) contested 183. On the basis of the coalition agreements published on the National Electoral Institute (INE) website, the party distribution of single-member seats would be as follows, with party single-member seat and vote shares in parentheses:
PAN – 72 (24.0%; 18.3%)
PRI – 30 (10.0%; 17.8%)
PRD – 7 (2.3%; 3.7%)
PVEM – 30 (10.0%; 5.5%)
PT – 31 (10.3%; 3.3%)
MC – 7 (2.3%; 7.0%)
MORENA – 123 (41.0%; 34.0%)
PES – 0 (0.0%; 2.7%)
RSP – 0 (0.0%; 1.8%)
FXM – 0 (0.0%; 2.5%)
Independents – 0 (0.0%; 0.1%)
The coalition seat and percentage totals, including votes and mandates won by their respective constituent parties running alone, are as follows:
PAN-PRI-PRD – 109 (36.3%; 39.7%)
PVEM-PT-MORENA – 184 (61.3%; 42.7%)
The absence of PVEM-PT-MORENA and PAN-PRI-PRD coalition candidates in many districts made little difference in the overall election outcome. Had both coalitions ran in all 300 districts, the MORENA-led coalition would have had a net loss of just four seats, gained by the PAN-led coalition.
Meanwhile, the official allocation of PR list seats won’t be known until as late as the third week of August, but on the basis of preliminary figures it would be as follows:
PAN – 41
PRI – 40
PRD – 8
PVEM – 12
PT – 7
MC – 16
MORENA – 76
PES – 0
RSP – 0
FXM – 0
Consequently, the overall composition of the Chamber of Deputies would be as follows (seat shares in parentheses):
PAN: 72 + 41 = 113 (22.6%)
PRI: 30 + 40 = 70 (14.0%)
PRD: 7 + 8 = 15 (3.0%)
PVEM: 30 + 12 = 42 (8.4%)
PT: 31 + 7 = 38 (7.6%)
MC: 7 + 16 = 23 (4.6%)
MORENA: 123 + 76 = 199 (39.8%)
Therefore, the coalitions would have the following totals:
PAN-PRI-PRD: 109 + 89 = 198 (39.6%)
PVEM-PT-MORENA: 184 + 95 = 279 (55.8%)
Since no party hit the 8% disparity cap, Mexico’s Chamber of Deputies electoral system operated in a purely parallel manner in this year’s election. Moreover, the JHH coalition parties won between themselves 47.76% of the “effective national vote” cast for parties entitled to take part in the allocation of PR seats. As such, the parties’ joint share of 55.8% of the Chamber seats happened to be just 8.04% above their effective national vote aggregate percentage. Had PR list seats been distributed among coalitions (as opposed to individual parties), the application of the 8% disparity cap would have reduced their overall seat total by only a single mandate.
Finally, the over-representation of the PVEM-PT-MORENA coalition in the Chamber of Deputies – where it retained a reduced but comfortable majority – stems largely from its continued dominance in twelve states in southern Mexico, where it won 85 of 99 single-member seats (85.9%) with 49.1% of the vote, while the PAN-PRI-PRD coalition trailed well behind with 32.9% of the vote and 14 seats (14.1%). In the rest of the country the election was closely fought, and while the VPM coalition parties won the popular vote, 43.5% to 39.2% for the JHH coalition partners, the latter still won slightly more district seats (99) than the former (95). Meanwhile, MC won all its seven district seats in Jalisco state, where it topped the poll with 31.5%, in a close three-way race with the PAN-PRI-PRD and PVEM-PT-MORENA coalitions, which polled 31.3% and 28.6%, respectively.
First of all, thanks again for promoting my comment: I’m very pleased to know that you found it interesting.
As expected, Mexico’s district tallies of last Sunday’s election – 100% complete since Friday morning – brought few changes to the distribution of Chamber of Deputies mandates: only two SMD seats changed hands compared to preliminary results of the election, from PAN-PRI-PRD (both from PAN) to PVEM-PT-MORENA (one for PVEM and another for PT). Moreover – and as noted on a previous comment on the site – this year the National Electoral Institute (INE) checked the “effective affiliation” of single-member district coalition candidates, to clamp down on attempts at gaming the 8% disparity cap by listing a different party affiliation in the coalition agreement. As a result, two SMD seats originally allocated to PRD were reassigned to PAN and PRI, while another two assigned to MORENA went instead to PVEM and PT.
With the aforementioned changes, the overall distribution of Chamber of Deputies SMD + PR list seats would be as follows (with seat and party vote shares in parentheses):
PAN: 71 + 41 = 112 (22.4%; 18.2%)
PRI: 31 + 40 = 71 (14.2%; 17.7%)
PRD: 5 + 8 = 13 (2.6%; 3.6%)
PVEM: 32 + 12 = 44 (8.8%; 5.4%)
PT: 33 + 7 = 40 (8.0%; 3.2%)
MC: 7 + 16 = 23 (4.6%; 7.0%)
MORENA: 121 + 76 = 197 (39.4%; 34.1%)
PES: 0 (0.0%; 2.8%)
RSP: 0 (0.0%; 1.8%)
FXM: 0 (0.0%; 2.5%)
Independents: 0 (0.0%; 0.1%)
Consequently, the coalitions had the following results:
PAN-PRI-PRD: 107 + 89 = 196 (39.2%; 39.6%)
PVEM-PT-MORENA: 186 + 95 = 281 (56.2%; 42.8%)
The JHH coalition parties won between themselves 47.84% of the “effective national vote” cast for parties entitled to take part in the allocation of PR list seats, and their joint share of 56.2% of the Chamber seats stood just 8.36% above their effective national vote aggregate percentage. Had PR list seats been distributed among coalitions (instead of individual parties), the application of the 8% disparity cap would have reduced their overall seat total by just two mandates.
Acuerdo INE/CG466/2021 (in Spanish and in PDF format) lists INE’s assignment of PAN-PRI-PRD and PVEM-PT-MORENA single-member district nominees among their respective constituent parties, after having determined their effective party affiliation.
By the way, in Mexico deputies elected under a bogus party affiliation are known as “diputados cachirules” (in Mexican Spanish “cachirul” means literally “person who pretends to be something he is not.”)
In Mexican elections party vote shares are usually calculated over the total number of votes cast, including void ballots. However, the 3% Chamber PR and party registration threshold is determined over valid votes only, and on that basis party vote shares were as follows:
PAN – 18.9%
PRI – 18.4%
PRD – 3.8%
PVEM – 5.6%
PT – 3.4%
MC – 7.3%
MORENA – 35.3%
PES – 2.9%
RSP – 1.8%
FXM – 2.6%
Independents – 0.1%
As such, PES, RSP and FXM were excluded from the distribution of Chamber PR list seats and are set to lose their registration, barring a successful challenge of election results in the Electoral Tribunal (TEPJF). If the results stand, this would be the second election in a row the staunchly social conservative Solidarity Encounter Party (PES; previously the Social Encounter Party) loses its registration.
Finally, while the lack of coalition agreements in many districts made little difference nationwide, at the regional level there was a more noticeable impact. In the first and second Chamber multi-member constituencies, which cover Mexico’s sixteen northern states, the PAN-PRI-PRD coalition won a clear majority of the popular vote, which however failed to translate into a majority of seats, as detailed below.
PAN-PRI-PRD: 43.4%, 56 seats
PVEM-PT-MORENA: 36.7%, 59 seats
MC: 10.7%, 7 seats
As it was, 52 of 122 districts in the northern states had no PAN-PRI-PRD coalition candidate, while just 39 districts had no PVEM-PT-MORENA coalition nominee; in those districts the coalitions’ constituent parties ran separately. As a result, the MORENA-led coalition had a net loss of just one seat with respect to 2018. Had both coalitions fielded candidates in all 122 districts, the PAN-led coalition would have won 63 seats to 52 for the MORENA-led coalition.
On the flip side, most of the seat gains by the PAN-PRI-PRD coalition came from Mexico City and the states of Colima, Mexico and Michoacán, where it won 38 of 79 seats with 43.1% of the vote to 41 for PVEM-PT-MORENA, which polled 43.2%. In 2018 the PAN-led coalition won just four seats in the capital and the aforementioned states, while the PRI-led coalition secured only three; the MORENA-led coalition swept in the remaining 72 districts. However, in 2021 PAN-PRI-PRD coalition candidates stood in 61 districts, while PVEM-PT-MORENA contested only 33. Had both coalitions ran in all 79 districts, the MORENA-led coalition would have won 47 seats to 32 for the PAN-led coalition.
Meanwhile, in the remaining twelve states of southern Mexico, the MORENA-led coalition remained overwhelmingly dominant with 86 of 99 seats, down just two from 88 in 2018. Despite setbacks in Mexico City, Mexico state, Michoacán and Colima, the south – comprising the third, fourth and fifth Chamber multi-member constituencies – continued to favor decisively the ruling party and its allies, as shown below.
PVEM-PT-MORENA: 46.6%, 127 seats
PAN-PRI-PRD: 37.2%, 51 seats
MC: 4.7%, no seats
What would Mexico’s election result had been if it had used a MMP system instead of MMM? Would there had been any difference?
Does a MMM or MMP or somewhere inbetween with a single vote have problems with decoy lists?
What is the reason for the 8% cap?
President Lopez Obrador has proposed a fairly dramatic change to Mexico’s electoral system. There are no English-language stories as of yet, but as usual you can get the gist from this Spanish story using Google Translate. The proposal appears to be to reduce the size of the Chamber of Deputies from 500 to 300 and the Senate from 128 to 96.
The story suggests that originally the proposal was to have all 300 members of the Chamber elected in single-member districts, but that instead the final document proposes that they be elected using state-wide lists. Mexico has 32 states, so this would mean an average district magnitude of about 9-10. It’s not clear how the Senate would be elected. The current system allocates two senators per state to the party which wins the most votes and one to the party which wins the second-most, and elects 32 on the basis of a nationwide list, so there are a number of ways in which the total could be cut by the needed figure.
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For anyone interested in reading the whole proposal, it’s available here . I’ve converted it to text using OCR, and that’s available here . As far as I can ascertain, the Senate change will involve electing three senators per state using party-list PR.
Thanks. I will give it a read (in Spanish).