plunk inflation

Batters are being hit by pitches this season at a rate of about .734 per game, which is down slightly from the past two years. When Craig Biggio entered the league in 1988, league wide plunks per game were around .438 but they have steadily increased throughout his career. The HBP per game numbers from 2001 through this year have been in a range not seen in 100 years. 2001's .778 plunks per game was the first to brake .700 since 1902 when it was .705.
Craig Biggio's and Hughie Jennings stats are more beneficiaries than causes of this trend, and removing their numbers from the overall stats does not impact the league wide totals too greatly.
During the span of Biggio's career (through 2004), there have been .598 HBPs per game, slightly better than the average during Hughie Jennings career, .550. Don Baylor's era was relatively plunk-free with .374 hit batters per game.

year	hbp/gm		year	hbp/gm	year	hbp/gm	year	hbp/gm
2004	0.762		1973	0.389	1943	0.267	1913	0.569
2003	0.761		1972	0.404	1942	0.278	1912	0.589
2002	0.72		1971	0.424	1941	0.252	1911	0.686
2001	0.778		1970	0.425	1940	0.288	1910	0.658
2000	0.647		1969	0.454	1939	0.29	1909	0.639
1999	0.651		1968	0.481	1938	0.288	1908	0.625
1998	0.651		1967	0.464	1937	0.26	1907	0.653
1997	0.639		1966	0.423	1936	0.336	1906	0.641
1996	0.62		1965	0.445	1935	0.313	1905	0.68
1995	0.605		1964	0.428	1934	0.281	1904	0.665
1994	0.548		1963	0.441	1933	0.29	1903	0.686
1993	0.529		1962	0.438	1932	0.299	1902	0.705
1992	0.465		1961	0.403	1931	0.302	1901	0.81
1991	0.43		1960	0.396	1930	0.325	1900	0.969
1990	0.409		1959	0.402	1929	0.331	1899	1.01
1989	0.381		1958	0.405	1928	0.375	1898	0.997
1988	0.438		1957	0.415	1927	0.394	1897	0.978
1987	0.4		1956	0.39	1926	0.392	1896	0.032
1986	0.386		1955	0.405	1925	0.409	1895	0.017
1985	0.333		1954	0.358	1924	0.448	1894	0.019
1984	0.317		1953	0.396	1923	0.489	1893	0.049
1983	0.34		1952	0.392	1922	0.495	1892	0.04
1982	0.321		1951	0.364	1921	0.46	1891	0.059
1981	0.334		1950	0.355	1920	0.445	1890	0.541
1980	0.313		1949	0.301	1919	0.475	1889	0.301
1979	0.36		1948	0.274	1918	0.455	1888	0.324
1978	0.367		1947	0.248	1917	0.469	1887	0.734
1977	0.376		1946	0.255	1916	0.513	1886	0.307
1976	0.353		1945	0.291	1915	0.55	1885	0.376
1975	0.394		1944	0.276	1914	0.546	1884	0.314
1974	0.399