[EM] Definition of proportional electoral system

[Luděk Belán]

Thank you for answer.
I didn't express myself accurately. I wanted to know whether the mentioned 
principle is a necessary condition of a proportional electoral system, not a
sufficient condition.




Luděk Belán


---------- Původní e-mail ----------
Od: Kristofer Munsterhjelm <km_elmet at t-online.de>
Komu: Luděk Belán <LudekBelan at seznam.cz>, election-methods at electorama.com
Datum: 28. 8. 2023 13:23:10
Předmět: Re: [EM] Definition of proportional electoral system
"On 8/28/23 12:13, Luděk Belán wrote: 
> Dear all, 
> excuse my bad English. 
> 
> Can the principle that /if party "A" gets more votes than party "B" then 
> party "A" must not get fewer mandates than party "B"/ be considered a 
> defining characteristic of a proportional electoral system? 

It doesn't need to imply propoprtionality. Consider the following method: 

The first party (by vote count) gets 90% of the seats (mandates). 
The second party gets 5%. 
The third party gets 2.5% 
The fourth party gets 1.25% 
The fifth party also gets 1.25% 
The rest get nothing. 

This is usually not proportional, but if A gets more votes than B, A can 
never get fewer seats than B, so it passes your principle. 

Most proportional methods would pass your principle, though. 

Note that some fail a related principle that "if some people change 
their mind and vote for party B instead of A, then A shouldn't gain 
seats at the expense of B". That's called population-pair monotonicity 
or vote-ratio monotonicity. Wikipedia has an article about it here: 
https://en.wikipedia.org/wiki/Vote-ratio_monotonicity 

-km 
"
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