How does the highest-average rule distribute seats among political parties?

The highest-average rule, also known as the largest-average formula, distributes legislative seats sequentially by awarding them one at a time to the party with the highest average number of votes.1

To calculate this average, a party's total votes are divided by a divisor that increases each time the party is awarded a seat. The specific divisor used depends on the method:

• d’Hondt method: The divisor is the number of seats already won plus one. After the first seat is awarded, the party's vote total is divided by two, then three, and so on. This method tends to favor larger parties.1
• Sainte-Laguë method: This method uses only odd numbers as divisors. After winning the first seat, the vote total is divided by three, then five, and so on. This approach is generally more favorable to middle-sized parties.1

Under these systems, the first seat is always awarded to the party with the highest absolute number of votes, as no seats have yet been allocated to serve as divisors.1