Defects in the various "pure" P.R. systems
Any at large system
No local candidates possible. Multiple very limited special interest winners
Any multi-member district system
Fewer parties getting representation. Gerrymander possible depending on
Nominations are not needed (either by a party elite or by party members)
since candidates could get on ballot directly by nominating petition.
Possibility of no local candidates with at large lists. Votes per seat
between party winners will be unequal due to seat apportionment formula
(especially if few seats). Any threshold can cause wasted votes (if no
additional choices allowed).
Mixed Member (MM)
Gerrymander continues for single member district seats. Possibility of wasted
votes if party is overrepresented due to excessive number of single member
district winners. See also List System defects.
Preference Voting (PV)
If Droop Quota is used, then wasted votes of roughly 100 percent/(seats +1).
Wasted votes if no additional choices made with surplus votes to be
transferred (especially if small number of seats in district). Condorcet
violation likely if small number of seats in district. Random factor if
random surplus votes transferred. Votes needed to win the last or the last
few seats will be less than for the first winner due to nontransferred votes.
Gerrymander possible due to votes per seat ratios of parties in different
districts will be unequal.
Condorcet violation possible if small number of seats in district.
Defects in Single Winner Systems
Majority Preference Voting (MPV)
Condorcet and/or approval voting violations highly possible by dropping out
lowest vote receiver who may be majority compromise choice.
Based on relative comparisons and not absolute approval or disapproval
(especially for second and later choices). Circular result ties possible in
Approval Voting (AV)
Based on absolute approval or disapproval. No relative comparisons among
multiple majority winners.