What electoral system is being used?
No formal threshold whatsoever on constituency level; it varies depending on district magnitude (using a simple calculation of 100%/the # of members elected). On national level, parties need to get at least 3 percent in at least a fifth of all states to win seats anywhere. Everywhere, there is a closed-list proportional representation, which translates into stronger parties in practice. Internal primaries are generally used to determine who fills list positions in each state, but this is far from universal.
More generally, all the vote counting is done on state level, but rules are uniform and decided on national level. The votes of parties that fail to reach either threshold are discounted entirely for purpose of seat allocation, unless party leadership has decided where they will go (the Greens refusing to do this in 2017 has been cited as a major factor in the right's narrow victory). Despite this transfer mechanic, these rules can still result in disproportionate results in states dominated by a particular party.
This status quo favors bigger parties as well as those with broad national appeal and distinctly disfavors small, newer ones, such as the Greens.
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