The data is league-wide and is a cumulative sum of the following terms: 1B/AB, 2*2B/AB, 3*3B/AB, 4*HR/AB (1B=single, 2B=double, 3B=triple, HR=home run, AB=at bat). Note that the American League data does not start until the creation of the American League in 1901.

Historical Major League Baseball data is freely available from many sources online. This data was taken from Baseball-Reference.com [1] [2] (accessed June 1, 2008)

The file was created in Gnuplot with the following code:

set terminal svg enhanced size 640 480 fname "Helvetica" fsize 12
set output "MLB_slugging_history.svg"
set style line 1 linetype 1 pointtype 0 linewidth 2 linecolor 6
set style line 2 linetype 1 pointtype 0 linewidth 2 linecolor 7
set style line 3 linetype 1 pointtype 0 linewidth 2 linecolor 8
set style line 4 linetype 1 pointtype 0 linewidth 2 linecolor 2 
set style line 5 linetype 1 pointtype 0 linewidth 2 linecolor 21
set style line 6 linetype 1 pointtype 0 linewidth 2 linecolor 11
set style line 7 linetype 1 pointtype 0 linewidth 2 linecolor 17
set style line 8 linetype 1 pointtype 0 linewidth 2 linecolor 9
set xrange [1890:2008]
set yrange [0:0.5]
set format y "%.3f"
set xlabel "Year"
set ylabel "Contribution to slugging average"
set key top center horizontal 
plot \
"[datafile1]" u 1:(4*$15+3*$14+2*$13+$12) t "HR"   w filledcurves x1 linestyle 1, \
"[datafile1]" u 1:(      3*$14+2*$13+$12) t "3B"   w filledcurves x1 linestyle 2, \
"[datafile1]" u 1:(            2*$13+$12) t "2B"   w filledcurves x1 linestyle 3, \
"[datafile1]" u 1:(                  $12) t "1B "  w filledcurves x1 linestyle 4, \
"[datafile2]" u 1:(4*$15+3*$14+2*$13+$12) notitle w filledcurves x1 linestyle 5, \
"[datafile2]" u 1:(      3*$14+2*$13+$12) notitle w filledcurves x1 linestyle 6, \
"[datafile2]" u 1:(            2*$13+$12) notitle w filledcurves x1 linestyle 7, \
"[datafile2]" u 1:(                  $12) notitle w filledcurves x1 linestyle 8

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