Switch Hitter righty/lefty splits.

Entire Careers, From 1901 to 2013, Switch-hitter, (requiring onbase_plus_slugging>=.8 and At least 7500 plate appearances), sorted by greatest On-Base Plus Slugging:

Rk	Player	OPS	PA	From	To	Age	G	AB	R	H	2B	3B	HR	RBI	BB	IBB	SO	HBP	SH	SF	GDP	SB	CS	BA	OBP	SLG	Pos	Tm
1	Mickey Mantle	.977	9907	1951	1968	19-36	2401	8102	1676	2415	344	72	536	1509	1733	126	1710	13	14	47	113	153	38	.298	.421	.557	*8397/645	NYY
2	Lance Berkman	.954	7564	1999	2013	23-37	1817	6271	1124	1857	417	29	361	1208	1171	158	1254	66	1	54	141	86	48	.296	.409	.545	3798/D	HOU-TOT-STL-TEX
3	Chipper Jones	.930	10614	1993	2012	21-40	2499	8984	1619	2726	549	38	468	1623	1512	177	1409	18	3	97	253	150	46	.303	.401	.529	*57/6D9	ATL
4	Bernie Williams	.858	9053	1991	2006	22-37	2076	7869	1366	2336	449	55	287	1257	1069	97	1212	39	12	64	223	147	87	.297	.381	.477	*8D/97	NYY
5	Carlos Beltran	.855	8388	1998	2013	21-36	1931	7350	1270	2072	416	74	335	1251	899	92	1343	39	17	83	141	306	47	.282	.360	.495	*89/D7	KCR-NYM-TOT-STL
6	Reggie Smith	.855	8051	1966	1982	21-37	1987	7033	1123	2020	363	57	314	1092	890	115	1030	33	8	86	150	137	86	.287	.366	.489	983/5D47	BOS-STL-TOT-LAD-SFG
7	Eddie Murray	.836	12817	1977	1997	21-41	3026	11336	1627	3255	560	35	504	1917	1333	222	1516	18	2	128	315	110	43	.287	.359	.476	*3D/57	BAL-LAD-NYM-CLE-TOT
8	Bobby Bonilla	.829	8257	1986	2001	23-38	2113	7213	1084	2010	408	61	287	1173	912	128	1204	28	5	97	169	45	57	.279	.358	.472	5973/D81	PIT-NYM-TOT-BAL-FLA-ATL-STL
9	Ken Singleton	.824	8559	1970	1984	23-37	2082	7189	985	2029	317	25	246	1065	1263	125	1246	17	29	60	248	21	36	.282	.388	.436	*9D7/8	NYM-MON-BAL
10	Roberto Alomar	.814	10400	1988	2004	20-36	2379	9073	1508	2724	504	80	210	1134	1032	62	1140	50	148	97	206	474	114	.300	.371	.443	*4/D6	SDP-TOR-BAL-CLE-NYM-TOT
11	Chili Davis	.811	9997	1981	1999	21-39	2436	8673	1240	2380	424	30	350	1372	1194	188	1698	15	20	94	232	142	98	.274	.360	.451	D897/13	SFG-CAL-MIN-KCR-NYY
12	Tim Raines	.810	10359	1979	2002	19-42	2502	8872	1571	2605	430	113	170	980	1330	148	966	42	39	76	142	808	146	.294	.385	.425	*78D/49	MON-CHW-NYY-OAK-TOT-FLA
13	Frankie Frisch	.801	10099	1919	1937	20-38	2311	9112	1532	2880	466	138	105	1244	728		272	31	229		55	419	74	.316	.369	.432	*45/6	NYG-STL

Provided by Baseball-Reference.com: View Play Index Tool Used
Generated 4/15/2013.

Click this link to view my details of their splits.

Only Berkman throws lefty.  I'll look at the top ten and compare them against themselves to try to get an idea of whether switch hitting actually worked for them.

Excluded:
Mantle: vs RHP as RHB 1 G, 1 PA
Williams:
vs RHP as RHB 14 G, 23 PA, 19 AB, 1.014 OPS
vs LHP as LHB 1 G, 1 PA
Beltran: vs RHP as RHB 5 G, 6 PA, 6 AB
Murray: vs RHP as RHB 1 G, 1 PA
Bonilla:
vs RHP as RHB 13 G, 36 PA, 26 AB, .829 OPS
vs LHP as LHB 2 G, 5 PA, 5 AB
Alomar:
vs RHP as RHB 2 G, 2 PA, 2 AB
vs LHP as LHB 48 G, 90 PA, 81 AB, .667 OPS

Mantle actually had more PA batting righty against righty: two games against Hoyt Wilhelm and two PA against Emilio Hernandez.  So few are incidental.

Other than Mantle very little black ink (led league) among the other nine.

Mantle:
Runs 5
3B 1
HR 4
RBI 1
BB 5
SO 5
BA 1
OBP 3
SLG 4
OPS 6
OPS+ 8
TB 3
MVP 3

Berkman:
2B 2
RBI 1

Jones:
BA 1
OBP 1
OPS 1
OPS+ 1
MVP 1

Williams:
BA 1

Smith:
OBP 1
OPS+ 1
TB 1

Murray:
HR 1 (1981) short season
RBI 1 1981) short season
BB 1
OBP 1
OPS+ 1

Bonilla:
2B 1

Singleton:
OBP 1

Alomar:
Runs 1

Berkman was done backwards since he is the only lefty thrower.  Subtracted batting lefty from batting righty.  Since Mantle's averages were all lower batting lefty his percentages are positive but his HR/AB and SO/AB are both higher batting lefty so his percentages are negative.

BA OBP SLG OPS HR/AB SO/AB
Mantle 14.85% 1.18% 5.04% 3.40% -19.69% -49.45% Mantle
Berkman 18.08% 16.85% 40.96% 29.73% 51.89% 11.38% Berkman
Jones 0.33% -3.58% -8.63% -6.52% 24.51% -2.38% Jones
Williams 5.19% 6.05% 7.55% 6.78% -31.36% 12.40% Williams
Beltran 4.45% 0.00% 8.33% 4.95% -16.53% 2.83% Beltran
Smith 0.35% -3.07% -10.55% -7.26% 39.99% -15.60% Smith
Murray -6.16% -8.53% -10.34% -9.55% 19.31% 15.35% Murray
Bonilla 1.42% -5.81% 1.05% -1.95% -11.17% 39.03% Bonilla
Singleton -11.92% -14.20% -15.86% -15.07% 23.04% -19.22% Singleton
Alomar -17.16% -14.54% -10.95% -12.72% -24.23% -53.89% Alomar
BA OBP SLG OPS HR/AB SO/AB

Mantle is way lower in BA batting lefty but that's about it.  Slugging is skewed because batting righty in Yankee Stadium pushed down his HR/AB batting righty and consequently his BB because they weren't as afraid that he would homer, which apparently drove up his lefty OBP but I'll examine Mantle in much more detail in subsequent posts.  Mantle's OPS difference is only 3.4%.

Williams and Beltran have similar patterns to Mantle without the Yankee Stadium bias, which was greatly reduced by the time Williams played for the Yankees.

Berkman was much worse batting righty.  He might have been better off just batting his natural lefty.  OPS difference is 30%!

Jones, Smith, Murray, Singleton, Alomar all  batted better lefty.  Bonilla is only slightly better lefty.  Here are their OPS differences:
Jones -6.52%
Smith -7.26%
Murray -9.55%
Bonilla -1.95%
Singleton -15.07%
Alomar -12.72%

Click this link to view "census" years data from retrosheet.org: 1950, 1960, 1970, 1980, 1990, 2000, 2010.  retrosheet.org uses different abbreviations from baseball-reference.com.  Here are the averages for those seven seasons.

LH v RP RH v LP RH v RP LH v LP
0.270 0.266 0.253 0.244    BA
0.347 0.336 0.317 0.316    OBP
0.412 0.408 0.387 0.360    SLG
0.758 0.744 0.704 0.677    OPS
31.59% 22.27% 38.81% 7.32%    percent AB

Lefty batter against lefty pitcher loses all the averages, which is probably why it has the lowest percent of AB: 7.3%.  So I guess it's understandable why Berkman decided to switch hit.  Lefty batter against righty pitcher wins all the averages.  Here's the pecking order:
LH v RP lefty batter against righty pitcher
RH v LP righty batter against lefty pitcher
RH v RP righty batter against righty pitcher
LH v LP lefty batter against lefty pitcher

Excluding Berkman we know what these nine natural righty batters did against lefty pitchers, second in the pecking order.  By switch hitting, for over 70% of their PA they moved up to the top spot against rather than drop one spot in the pecking order. For OPS, rather than drop from .744 to .704, they increased to .758.  The switch hitters needed to beat the percentage difference:

(.744 - .704)/.744 = 5.38%  decrease for righty batter against righty pitcher

(.758 - .744)/.744 = 1.88%.  increase for lefty batter against righty pitcher

The benefit appears to be more avoiding the 5.38% drop rather the 1.88% increase.  Could we say that the cumulative difference is the sum of those percentages, about 7.26% applied to the roughly 72% of PA?  Remember, that's based on all MLB batters for seven sample seasons from 1950 through 2010.  Here are the percentage differences from (righty batter against lefty pitcher):

LH v RP RH v RP     Total
1.50% -4.89% BA     6.39%
3.27% -5.65% OPB     8.93%
0.98% -5.15% SLG     6.13%
1.88% -5.38% OPS     7.26%

I'm not going to compute that for them because, frankly, they're not that interesting.  I'll do it in detail for Mickey Mantle.