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Goal difference or points difference is a form of tiebreaker used to rank sport teams which finish on equal points in a league competition. Either "goal difference" or "points difference" is used, depending on whether matches are scored by goals (as in ice hockey and association football) or by points (as in rugby union and basketball). Goal difference (or points difference) is calculated as the number of goals (or points) scored in all league matches minus the number of goals or points conceded. Goal difference was first introduced as a tiebreaker in association football, at the 1970 FIFA World Cup, and was adopted by the Football League in England five years later.〔 It has since spread to many other competitions, where it is typically used as either the first or, after tying teams' head-to-head records, second tiebreaker. Goal difference has often replaced the older goal average, or goal ratio. Goal average means the number of goals scored divided by the number of goals conceded. It was replaced by goal difference, which was thought to encourage more attacking play, encouraging teams to score more goals (or points) as opposed to defending against conceding.〔 However goal average is still used as the tiebreaker in Australian rules football where it is referred to as "percentage". This is calculated as points scored divided by points conceded, and then multiplied by 100.〔(【引用サイトリンク】url=http://thepowerfromport2.tripod.com/AFL/calculatingpercentages.html )〕 If two or more teams' total points scored and goal differences are both equal, then often goals scored is used as a further tiebreaker, with the team scoring the most goals winning.〔(【引用サイトリンク】url=http://www.premierleague.com/en-gb/fans/faqs/who-wins-league-if-teams-finish-on-same-points.html )〕 After this a variety of other tiebreakers may be used. ==Goal difference ''v.'' goal average== The different schemes can lead to strikingly different results. With the following matches: ---- ---- Under goal average, Team A would win: |- style="background:#ccffcc;" | 1 || style="text-align:left;"|Team A || 2 || 1 || 0 || 1 || 3 || 1 || 3.000 || 3 |- | 2 || style="text-align:left;"|Team B || 2 || 1 || 0 || 1 || 6 || 3 || 2.000 || 3 |- | 3 || style="text-align:left;"|Team C || 2 || 1 || 0 || 1 || 1 || 6 || 0.167 || 3 |} Under goal difference, Team B would win: |- style="background:#ccffcc;" | 1 || style="text-align:left;"|Team B || 2 || 1 || 0 || 1 || 6 || 3 || +3 || 3 |- | 2 || style="text-align:left;"|Team A || 2 || 1 || 0 || 1 || 3 || 1 || +2 || 3 |- | 3 || style="text-align:left;"|Team C || 2 || 1 || 0 || 1 || 1 || 6 || −5 || 3 |} Goal average was replaced by goal difference due to the former's encouragement of lower-scoring games. For example, a team that scores 70 while conceding 40 would have a lesser goal average (1.750) than another team that scores 69 while conceding 39 (1.769). Or, for the team that has scored 70 while conceding 40, conceding another would reduce the goal average by 0.043 (to 1.707), whereas scoring another would increase it by only 0.025 (to 1.775), making not conceding much more important than scoring again. Another issue with goal average is that, if a team has conceded no goals (e.g. Group 1 of the 1966 World Cup), the value cannot be calculated, as division by zero is undefined. In this case, the only option is to treat the value as equal to infinity. This means that a goal average with no goals conceded would be better than a goal average with one or more goals conceded: for example, 2–0 would be better than 3–1. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Goal difference」の詳細全文を読む スポンサード リンク
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