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# Terminology

## ROI

ROI - is a key indicator in sports betting, which measures player's bets profitability. This abbreviation came to betting from the financial sector and stands for Return of Investment. From a business point of view, you can imagine that every bet is your investment, and the net gain is profit. Their ratio, expressed as a percentage, will be ROI.

Example:
Let's say we made one bet of 10€ on odds 1.5 and won. Our income in this case will be 15€, and profit, accordingly, 5€. To calculate ROI, you need to divide the profit by the amount of the bet and then multiply by 100%.
Let’s calculate result: 5 ÷ 10 × 100% = 50% ROI.

In order to calculate the ROI of several bets, you need make a sum of all bets and divide the total profit by this number. It is very important for every professional to track the ROI statistics of their bets and adjust the strategy if this indicator becomes negative. The optimal value of ROI at a long distance of more than 1000 bets is considered to be 5-7%.

## Value bet

Value bet - the value, that determines the expected profitability of the prediction, expressed as a percentage. Bets with a positive Value bet always have higher chances to win comparing to probabilities in the odds on offer from a bookmaker.

Example:
Let’s consider match Wolverhampton - Leicester City. Probability of outcome Both to score, according to our calculations, is 61%. The maximum coefficient offered by the bookmaker is 1.97, in order to find out odds probability, we will use the formula 1 ÷ 1.97 × 100% = 51%. Then to calculate the Value bet, you need to find the difference between two probabilities. 61% - 51% = 10%.

Often, people confuse the concepts of value bet and ROI. Let’s say that using Value bet we evaluate our bet before the match, and with ROI after. In a perfect world each bet with a Value bet of 10% should bring us 10% ROI.

## Error

Error - a value that determines the possible probability deviation of our odds line calculations, also expressed as a percentage. This indicator was created by the developers of xGscore to filter and select profitable outcomes for predictions. The smaller the outcome error value, the more likely we correctly calculated its Value bet.

Example:
Let’s consider match Celta - Real Madrid. Our prediction is Real Madrid’s win with a probability of 60%. To calculate the error, we need to refer to the «Teams impact» slider on the match page. Our calculations determined the impact of the teams as 50 to 50. If you move the slider all the way to the left, making the impact of Real 100%, you can see that the probability of their winning has increased to 65%. Then, if you set the Celta’s impact to 100%, Real Madrid’s chance of winning drops to almost 55%. These changes indicate the outcome probability error. When calculating odds chances, we take the average value between 65% and 55%, that is, 60%. Thus, the error of this outcome is +/- 5%.

It is worth noting that in our predictions the error may differ slightly from example above. Since its calculations depend on several other secondary factors, but the main thing is still the impact of the teams. According to our bets statistics, predictions with the smallest error give the highest ROI. Therefore, you should always pay attention to this value when choosing an outcome for a bet.