Maybe Dogboy can answer this one as Ive never seen a definitive explanation to this question:
Over how many spins is the RTP calculated? Ive seen some say 'over the lifetime of the machine' but that seems to suggest that one year it might pay out 81% and the next year 110% and still be in the 95% range...?? Ive also heard that its based on the reel positions and how many possible combinations there are in the game...i.e. if there are 150,000 combinations and only one jackpot combination, then you can expect it to happen about once in 150,000 spins.....but could happen also at spin 299,998 and 299,999 and still be on track at spin 300,000 (hope that makes sense)
Dogboy...hellllppp!!
Heya,
RTP on a random spinning reel slot in its basic form is a calculation based on 1 cycle, this being the total number of possible combinations, if each possible combination spun in once only during that cycle.
An example is probably the easiest way to explain it:
Suppose you have a slot with 30 positions on each reel (for ease of calculation). The game's cycle is 30^5, so there are 24,300,000 possible combinations that could appear on a given spin.
Each combination represents a single order of stop positions on the reels. So, for example, based on 5 random requests for a result (one for each reel):
Stop position 13 (reel 1), followed by stop position 11 (reel 2), followed by stop position 18 (reel 3), followed by stop position 3 (reel 4), followed by stop position 30 (reel 5)
So there are 24.3M possible ways the 5 reels could line up.
Different symbols may appear on different reels more than once, so you could get repetition of possible prize-winning combinations, e.g.: There may be 1 combination yielding 5 substitutes (if there is 1 wild on each reel), but there may be 20,000 ways of getting 5 of a lower symbol.
So, getting back to what RTP is:
The theoretical return to player is an exact value, but only if each possible combination (24.3M in the above example) occurs once, and once only, during a cycle, in this case 24.3M spins.
Since results are random, the same order could appear more than once, hence why real results differ from theoretical.
It is possible to calculate, using normal distribution and the game's standard deviation, a range of what most (but not all) RTP results will fall into over a given period of play.
95% of the area under a normal curve lies within roughly 1.96 standard deviations of the mean, so taking a popular, but unnamed, game as an example; 95% of results should fall within +/- 8.2% of theoretical RTP over 50,000 spins. Move that out to 250,000 spins and 95% of results should be within +/- 3.7%.
Over a shorter period of play results skew wildly. At 90% confidence (1.645 SD), this same game would have +/- 49.15%...so 90% of sets of 1000 spins should fall into a band from an RTP of 46.05% to 144.35%
However, even then, some results will fall outside an expected range, on either side of the scale
Features tend to increase volatility, which all affects expected RTP ranges over given periods of play.
Variables such as pick feature probability schedules still yield a prize range and an associated probability, so everything can still be built into a standard deviation prize table for calculation.
And as far as RTP goes for these, again it's just a certain number of trigger combinations will, according to a pick probability schedule, yield a certain prize.
Features that don't have pick schedules attached are simply another reel strip combinational calculation, with overall average return from the feature simply multiplied by the odds of triggering, or in the case of a retrigger feature that overall odds of being a feature game.
The important items to remember are:
1) RTP is a theoretical calculation based on a complete cycle without repetition
2) Random systems do not have any correlation between spins, so it is possible to achieve exactly the same combination on successive spins.
3) There will be massive swings away from expected RTP (on both a positive and negative end), especially over smaller periods of play
4) In relation to periods of play, 1000 spins on a slot on a given day isn't small to the player, 5000 is huge...but both are small statistically speaking
That's the beauty of randomness, but it can also bite.
Woooof