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A betting strategy or betting system is a structured approach to gambling intended to counter the inherent bias held by the house in casino and card games, by bookmakers in horseracing and sports betting, and other gambling situations. A successful strategy should increase the odds of winning in order to produce long term profits from a pursuit which under normal circumstances will only ever result in a long term loss.
All successful betting systems are predicated on statistical analysis, seeking to exploit the rare circumstances when the odds are in the favour of the player. Though the basis of all risk is fundamentally the same, betting systems vary in relation to the rules and circumstances of each particular game.
Well-known betting systems include:
- Card games – Card counting
- Roulette – Martingale
- Horse racing – Hedging, Arbitrage
- Sports – Handicapping
Independent events 
The following betting strategies apply to games which operate on independent events. For such games, the odds of a particular outcome are identical for every bet played. No such strategy can beat the house edge (if any) in the long run, and all of them trade off many small wins for a big loss or vice versa.
- Martingale – doubling bet after each loss until a win is achieved (or fails when the amount of the bet becomes excessive)
- Kelly criterion
- Split martingale
- Contra d'Alembert
- Paroli of Three
Horse racing systems 
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Horse racing betting systems are based on a number of criteria, some of which include analysis of the horses' form.
Often horse racing systems are based on financial systems such as hedging (betting on multiple outcomes in a race) and arbitrage (lay the horse a low price and back it at a high price). Other horse racing systems exist which are based on items such as horse name, jockey form, trainer form, and lane draw. Modern horse racing systems can rely on specific betting possibilities only offered on betting exchanges.
The ineffective independent event systems in the above section can also be applied to horse racing.