“In all electoral systems (and with legislated as well as voluntary candidate quotas), the quota provisions should include rules about the gendered rank order. Fair vertical placement of the female and male candidates on the electoral list (PR systems with closed party lists) and/or a horizontal distribution of both sexes in winnable seats is essential if women are to have a real chance of being elected. Rank-order rules are adopted to prevent quota rules (for instance a general rule of 30 or 50 per cent female candidates) from becoming merely symbolic, with only a few women getting elected because political parties have placed most of the female candidates at the bottom of the lists or in unwinnable constituencies. Many quota systems today combine rules about the total number of women and men on the candidate lists with specific rules concerning the gender composition of the top candidates […].[1] 

Examples of vertical rank-order rules for the distribution of female and male candidates are: 

• Zebra or zipper systems: alternating female and male candidates throughout the lists (e.g., Bolivia, Costa Rica, Ecuador, France, Kenya, Republic of Korea, Lesotho, Libya, Nicaragua, Senegal, Tunisia and Zimbabwe); alternation is used by many Green parties as well Social Democratic parties; 

• A requirement that the top two candidates are not of the same sex (e.g., Belgium); 

• 40:60 ratio for every five posts on the list (e.g., Spain); and 

• One out of every group of three candidates must be a woman (e.g., Albania, Argentina, Indonesia, Serbia, Timor-Leste).” [1]