EPL: Set Piece vs Open Play (09-10 to 15-16)

I decided to just run some basic analysis on open play and set piece shots/goals, just to have it out in public.  All data is from Opta and whoscored.com. As with many
things on whoscored, certain stats didn't add up but I deciphered the shots and goals into the proper situation and totals. Just so we are clear open play and set piece
are based on Opta's definition. Set piece shots and goals do not include penalties.

Reliability

First thing I like to look at is how reliable a metric is. Given that I only have the year over year stats, this how will we analyze the data.  

Reliability tells us to what degree we can expect a team to repeat its performance of a metric in the next season.

Open Play Shots For: 79% Skill vs 21% Luck

Set Piece Shots For: 68% Skill vs 32% Luck

We can do a good job of predicting each type of shot situation from one year to the next. If you are a good open play shot team this year
we can reasonably expect you will be good again next year. Same goes for set piece just with slightly less accuracy.

Now the reliability is good know when analyzing teams but we want to make sure that the metrics can explain and/or
predict things that lead to winning. In our case,  goals. 

Explaining Goals For

How well do open play/set piece shots explain goals for in the same season.

This is quite interesting.  Open play shots correlate strongly at the end of the season with goals while, surprisingly, set piece shots
have literally no correlation.  Basically, open play shots give you a significantly better indication of what teams scored the most
or least goals in a Premier League season.

Predicting Goals in yr2

Finally, we will see how well open play and set piece shots predict future goals. 

Again, we see open play shots providing us with a far superior correlation.  Set piece shots provide us with literally no insight into
future goal-scoring performance. 

This led me to wonder how reliable are set
piece and open play goals?  And how well do they correlate to with Total Goals? What about the conversion rates?

I am not going to plot these but here are the correlations:

Open Play Goals, yr2 vs yr1: r2 = 0.525

Set Piece Goals, yr2 vs yr1: r2 = 0.05

Total Goals yr1 vs Open Play Goals, yr1: r2 = 0.83

Total Goals yr1 vs Set Piece Goals, yr1: r2 = 0.21

Open Play Conv Rate, yr2 vs yr1: r2 = 0.243

Set Piece Conv Rate, yr2 vs yr1: r2 = 0.000

Thoughts

Focusing on open play looks to be the most efficient way to score goals and win football matches. They are more reliable, explanatory, and
predictable at every turn.

Call me Roberto Martinez but I am struggling to see the value in set pieces.  Not only do they not correlate with total goals but
set piece goals are highly, highly variable from one season to the next.  In fact, at best bet we can expect teams to revert right
back to the league average the following year.

Granted this is a very macro look at two sub-groups of shots but at first glance all I am seeing is how much more important open
play is in the Premier League.

Data

Here are the numbers I worked with so you can play around and replicate the findings above.

Year	Team	Set Piece	Total Open Play	Total Goals	Set Piece Goals	Total Open Play Goals	Open Play Conv Rate	Set Piece Conv Rate
09-10	Arsenal	164	492	79	16	56	0.114	0.098
09-10	Aston Villa	172	317	51	16	24	0.076	0.093
09-10	Birmingham	159	289	38	14	20	0.069	0.088
09-10	Blackburn	224	262	40	21	14	0.053	0.094
09-10	Bolton	218	336	46	20	14	0.042	0.092
09-10	Burnley	133	320	44	4	30	0.094	0.030
09-10	Chelsea	224	598	100	17	70	0.117	0.076
09-10	Everton	186	395	59	17	31	0.078	0.091
09-10	Fulham	151	308	43	9	20	0.065	0.060
09-10	Hull	132	248	39	12	11	0.044	0.091
09-10	Liverpool	175	464	60	14	39	0.084	0.080
09-10	Manchester City	159	362	74	21	46	0.127	0.132
09-10	Manchester United	153	534	76	13	57	0.107	0.085
09-10	Portsmouth	160	367	37	12	16	0.044	0.075
09-10	Stoke	203	197	34	14	16	0.081	0.069
09-10	Sunderland	131	304	48	9	29	0.095	0.069
09-10	Tottenham	210	468	67	17	48	0.103	0.081
09-10	West Ham	168	372	50	18	19	0.051	0.107
09-10	Wigan	156	396	37	10	24	0.061	0.064
09-10	Wolverhampton Wanderers	150	284	31	12	11	0.039	0.080
10-11	Arsenal	168	479	71	9	56	0.117	0.054
10-11	Aston Villa	158	342	46	9	31	0.091	0.057
10-11	Birmingham	137	262	41	16	15	0.057	0.117
10-11	Blackburn	182	269	43	18	22	0.082	0.099
10-11	Blackpool	152	371	59	17	25	0.067	0.112
10-11	Bolton	194	371	50	14	32	0.086	0.072
10-11	Chelsea	219	518	69	18	43	0.083	0.082
10-11	Everton	180	396	52	14	31	0.078	0.078
10-11	Fulham	150	394	53	17	24	0.061	0.113
10-11	Liverpool	147	428	61	11	38	0.089	0.075
10-11	Manchester City	143	394	58	13	37	0.094	0.091
10-11	Manchester United	150	463	76	13	58	0.125	0.087
10-11	Newcastle United	169	333	57	20	28	0.084	0.118
10-11	Stoke	221	258	46	18	21	0.081	0.081
10-11	Sunderland	135	392	43	8	29	0.074	0.059
10-11	Tottenham	203	446	54	12	35	0.078	0.059
10-11	West Bromwich Albion	166	425	58	11	33	0.078	0.066
10-11	West Ham	167	399	43	13	21	0.053	0.078
10-11	Wigan	123	385	36	9	25	0.065	0.073
10-11	Wolverhampton Wanderers	167	289	47	16	24	0.083	0.096
11-12	Arsenal	154	480	79	8	59	0.123	0.052
11-12	Aston Villa	150	285	39	3	29	0.102	0.020
11-12	Blackburn	159	286	47	19	18	0.063	0.119
11-12	Bolton	153	336	43	13	23	0.068	0.085
11-12	Chelsea	169	497	64	14	44	0.089	0.083
11-12	Everton	144	371	51	13	27	0.073	0.090
11-12	Fulham	131	406	45	9	29	0.071	0.069
11-12	Liverpool	170	491	45	14	24	0.049	0.082
11-12	Manchester City	156	574	93	19	63	0.110	0.122
11-12	Manchester United	166	469	89	18	58	0.124	0.108
11-12	Newcastle United	137	349	51	8	41	0.117	0.058
11-12	Norwich	143	369	53	16	33	0.089	0.112
11-12	Queens Park Rangers	140	396	43	11	26	0.066	0.079
11-12	Stoke	152	218	38	16	12	0.055	0.105
11-12	Sunderland	112	344	44	10	31	0.090	0.089
11-12	Swansea	113	353	45	7	29	0.082	0.062
11-12	Tottenham	170	526	66	9	51	0.097	0.053
11-12	West Bromwich Albion	142	399	47	15	25	0.063	0.106
11-12	Wigan	113	399	42	11	24	0.060	0.097
11-12	Wolverhampton Wanderers	125	344	42	9	26	0.076	0.072
12-13	Arsenal	119	473	69	12	52	0.110	0.101
12-13	Aston Villa	107	328	53	10	28	0.085	0.093
12-13	Chelsea	148	468	74	15	46	0.098	0.101
12-13	Everton	181	450	54	11	39	0.087	0.061
12-13	Fulham	106	348	45	8	31	0.089	0.075
12-13	Liverpool	170	564	68	11	50	0.089	0.065
12-13	Manchester City	164	489	66	14	44	0.090	0.085
12-13	Manchester United	131	422	84	22	50	0.118	0.168
12-13	Newcastle United	121	406	45	6	31	0.076	0.050
12-13	Norwich	130	281	43	17	19	0.068	0.131
12-13	Queens Park Rangers	131	365	35	5	19	0.052	0.038
12-13	Reading	122	267	41	13	24	0.090	0.107
12-13	Southampton	126	387	50	8	29	0.075	0.063
12-13	Stoke	149	236	37	15	11	0.047	0.101
12-13	Sunderland	128	285	43	11	20	0.070	0.086
12-13	Swansea	95	411	48	5	41	0.100	0.053
12-13	Tottenham	153	528	63	10	51	0.097	0.065
12-13	West Bromwich Albion	116	382	53	9	33	0.086	0.078
12-13	West Ham	163	326	44	12	26	0.080	0.074
12-13	Wigan	131	368	48	13	28	0.076	0.099
13-14	Arsenal	126	394	70	8	55	0.140	0.063
13-14	Aston Villa	83	344	42	7	25	0.073	0.084
13-14	Cardiff	136	281	30	13	16	0.057	0.096
13-14	Chelsea	135	550	71	15	47	0.085	0.111
13-14	Crystal Palace	120	288	34	8	17	0.059	0.067
13-14	Everton	125	433	62	12	39	0.090	0.096
13-14	Fulham	114	314	42	14	18	0.057	0.123
13-14	Hull	134	292	37	10	21	0.072	0.075
13-14	Liverpool	151	488	102	26	54	0.111	0.172
13-14	Manchester City	165	501	99	20	69	0.138	0.121
13-14	Manchester United	128	393	64	11	46	0.117	0.086
13-14	Newcastle United	132	444	42	8	30	0.068	0.061
13-14	Norwich	117	348	31	4	20	0.057	0.034
13-14	Southampton	132	399	53	12	36	0.090	0.091
13-14	Stoke	96	327	44	7	31	0.095	0.073
13-14	Sunderland	144	341	47	13	16	0.047	0.090
13-14	Swansea	99	392	48	10	32	0.082	0.101
13-14	Tottenham	129	452	53	11	31	0.069	0.085
13-14	West Bromwich Albion	136	348	43	6	31	0.089	0.044
13-14	West Ham	129	291	38	10	24	0.082	0.078
14-15	Arsenal	122	481	70	16	46	0.096	0.131
14-15	Aston Villa	119	297	32	10	19	0.064	0.084
14-15	Burnley	115	312	29	7	17	0.054	0.061
14-15	Chelsea	121	438	73	15	52	0.119	0.124
14-15	Crystal Palace	145	291	46	19	22	0.076	0.131
14-15	Everton	116	360	48	11	29	0.081	0.095
14-15	Hull	118	310	32	7	24	0.077	0.059
14-15	Leicester	130	323	50	12	25	0.077	0.092
14-15	Liverpool	123	461	50	6	35	0.076	0.049
14-15	Manchester City	136	526	85	12	60	0.114	0.088
14-15	Manchester United	121	387	61	12	44	0.114	0.099
14-15	Newcastle United	144	323	41	7	31	0.096	0.049
14-15	Queens Park Rangers	163	367	43	12	20	0.054	0.074
14-15	Southampton	126	381	49	6	41	0.108	0.048
14-15	Stoke	134	365	47	6	38	0.104	0.045
14-15	Sunderland	121	283	35	9	12	0.042	0.074
14-15	Swansea	103	321	44	4	36	0.112	0.039
14-15	Tottenham	132	390	58	15	36	0.092	0.114
14-15	West Bromwich Albion	118	288	37	19	14	0.049	0.161
14-15	West Ham	156	331	45	12	28	0.085	0.077
15-16	Arsenal	129	441	65	13	45	0.102	0.101
15-16	Aston Villa	109	269	28	7	11	0.041	0.064
15-16	Bournemouth	122	338	43	12	28	0.083	0.098
15-16	Chelsea	118	403	57	11	38	0.094	0.093
15-16	Crystal Palace	157	307	42	15	15	0.049	0.096
15-16	Everton	119	367	57	8	43	0.117	0.067
15-16	Leicester	147	362	67	11	46	0.127	0.075
15-16	Liverpool	142	485	63	15	44	0.091	0.106
15-16	Manchester City	167	440	72	14	51	0.116	0.084
15-16	Manchester United	114	313	48	7	34	0.109	0.061
15-16	Newcastle United	77	317	45	8	30	0.095	0.104
15-16	Norwich	115	302	40	10	25	0.083	0.087
15-16	Southampton	127	388	57	13	41	0.106	0.102
15-16	Stoke	96	317	40	6	29	0.091	0.063
15-16	Sunderland	128	308	45	15	25	0.081	0.117
15-16	Swansea	115	321	46	8	23	0.072	0.070
15-16	Tottenham	150	503	71	17	43	0.085	0.113
15-16	Watford	110	329	39	8	21	0.064	0.073
15-16	West Bromwich Albion	118	266	35	12	16	0.060	0.102
15-16	West Ham	171	383	66	16	42	0.110	0.094
	Average	142.7	375.8	52.1	12.1	32.2	0.086	0.085