Bias in ATP Tennis Grass Odds – Tennis Analysis Part 5

With only a small profit made over the past 5 years on grass for ATP tennis, we decided to take a closer look at the analysis. The table below shows the analysis of all our grass bets over the last five years for ATP, with a description to come

Grass	Prob	#Bets	#Wins	%Wins	$Bet	$Profit	%ROI
0	0.1	0	0	-	$-	$-	-
0.1	0.2	0	0	-	$-	$-	-
0.2	0.3	0	0	-	$-	$-	-
0.3	0.4	64	13	20.3%	$9,932.10	-$2,501.86	-25.2%
0.4	0.5	71	21	29.6%	$15,373.58	-$1,434.54	-9.3%
0.5	0.6	120	51	42.5%	$23,245.82	$403.27	1.7%
0.6	0.7	98	48	49.0%	$23,385.33	-$3,053.37	-13.1%
0.7	0.8	75	55	73.3%	$21,374.76	$3,572.91	16.7%
0.8	0.9	59	50	84.7%	$23,212.61	$2,944.06	12.7%
0.9	1	12	10	83.3%	$6,548.18	$223.71	3.4%
	TOTAL	499	248	49.7%	$123,072.38	$154.18	0.1%
Grass	Odds	#Bets	#Wins	%Wins	$Bet	$Profit	%ROI
1	1.4	59	52	88.1%	$22,090.22	$2,357.08	10.7%
1.4	1.7	99	67	67.7%	$24,957.82	$1,366.45	5.5%
1.7	2	57	35	61.4%	$12,641.54	$1,042.50	8.2%
2	2.25	63	22	34.9%	$13,595.17	-$3,051.67	-22.4%
2.25	2.5	43	21	48.8%	$10,571.04	$1,478.16	14.0%
2.5	3	48	21	43.8%	$13,061.99	$2,887.09	22.1%
3	4	76	23	30.3%	$15,166.38	-$347.96	-2.3%
4	6	49	7	14.3%	$9,663.55	-$4,252.81	-44.0%
6	10	5	0	0.0%	$1,324.65	-$1,324.65	-100.0%
10	50	0	0	-	$-	$-	-
	TOTAL	499	248	49.7%	$123,072.38	$154.18	0.1%

Clearly this shows something that has long been suggested, in that grass is a favourites game. No wonder Sampras, Federer and a stack of pre-modern era players continually win on the green top.

Our analysis suggests that only bets of 70%+ probability have been profitable. This accounted for 13.2% ROI, with 146 of the 499 bets in total (29%). Similarly, only betting on favourites (where the odds are less than 2.0) resulted in 215 bets with 8.0% ROI. Betting on underdogs at odds of 3.0 or more, or even 4.0 or more provided very bad returns. 54 bets at odds of 4.0 or more resulted in a 50.7% ROI loss, with only a win happening only one in 8 bets.

Clearly on grass, these bets should be avoided. Simply by not betting on large outsiders (4.0 or more) increases the return from 0.1% ROI up to 5.1% ROI which is very acceptable.

I will leave it up to the individual what bets one might want to take here, but I am contemplating writing it into the program that only bets of 70% or greater probability be suggested. Keep in mind that it is a very small sample size for grass, and this could be why part of the problem occurs.

Interestingly, if one were to bet $100 on all the favourites on grass over the past 5 years, then you would have turned over $141,000 for a profit of $4,797 which equates to 3.4% ROI. Should one have bet $100 on all the underdogs, then your $141,000 would have yielded a loss of $29,291 for a -20.8% ROI.

A big difference indeed. Similarly, if one was to bet to win $100, then betting on the favourites would have put you back $718,693 for a nice profit of $20,133 or a 2.8% ROI. Betting on the underdogs to win $100 would have seen you fork out $20,133 for a loss of $9,780 or -14.7% ROI.

Seems to me to be a very big bias there. Perhaps our probabilities are generally pretty right., however it is the bias in the results that is causing such skew. It is important of course, when looking at biases in results not to think that this bias will stay for the long term. Once people start realising that grass court tennis strongly favourites the better player, then the odds will start to accommodate for this.

It may take a while, but at this stage, only betting on strong favourites seems to be most profitable.

Let us know what you think in the comments below.

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