There are multiple types of selection methods, such as a k-way tournament, roulette wheel, stochastic universal sampling (SUS), rank, and random. In a k-way tournament, k random individuals are selected and their fitness scores are compared with each other . The best-scoring individual is selected as a parent and this process is repeated to select the second parent. Another popular method is roulette wheel, where the chances of an individual being selected are proportionate to its score . Just like a roulette wheel, the wedges on the wheel are the size of the individual score divided by the sum of all scores in that generation. A random number is generated, or the "wheel is spun", to pick the location on the wheel for the selection of the parent. This process is repeated for the other parent. Similarly, SUS is another wheel-based method, where instead of spinning the wheel twice, the wheel is spun once and two points on the wheel are chosen for the two parents . Another similar method to roulette wheel is rank selection, where the sizes of the wedges are proportionate to the ranking of the population, not the individual score . This can be beneficial in multiple circumstances, such as negative fitness scores or when the fitness scores are close together (leading to almost equal wedge sizes and no selection pressure).