I'd like to thank everyone for their feedback regarding my article on Caribbean players over at THT. I was especially interested in a note from Mike Cook who speculated that perhaps lower plate discipline is a product of coaching philosophy towards Caribbean players who are perhaps viewed as not as intelligent as non-Caribbeans. Another thought that was perhaps Caribbean players develop plate discipline over time since they're not exposed to advanced coaching as early in their careers.
As to the latter hypothesis I took a look at Caribbeans and non-Caribbeans from ages 20 through 41 and produced the following graph.
As you can see the difference between the two groups remains pretty steady as both groups age (the sample size gets pretty small for Caribbeans around age 39) and so I think we can discount the second hypothesis. If you're wondering why the walk rate climbs steadily almost to age 40 when generally performance declines as players reach their early thirties, keep in mind that this graph includes all players and so those players who are still playing in their mid to late thirties are "selected" via their better than average performance. In other words, the same set of players is not tracked at each age and so better players are represented on the right end of the graph.
As for the former hypothesis I wouldn't argue against the notion that Caribbean and Latin players may be viewed as less intelligent, primarily because of the language barrier. Moises Alou said as much during the Krueger controversy. However, since the realization that plate discipline is a skill unto itself is relatively new in baseball, I would argue that since the production of the two groups is basically equivalent, coaches in general see no need to focus on plate discipline with Caribbean players.
J.C. Bradbury of Sabernomics fame (who has several excellent articles in The Hardball Times Baseball Annual 2006-buy-yours-today) also made an interesting point when he noted that Caribbean players are less likely to be left-handed and more likely to be switch hitters. I admit that I remembered reading his post but forgot completely about it when putting together the article. Indeed, just as J.C. found, in my study 13.2% of Caribbean players were switch hitters and 14.4% left-handed hitters while for non-Caribbeans it was 7.2% and 28.8% respectively.
Caribbean Count Pct PA Pct
B 131 0.132 232865 0.215
R 717 0.724 705547 0.651
L 143 0.144 146075 0.135
Non-Caribbean Count Pct PA Pct
B 469 0.072 682139 0.116
R 4154 0.640 3221848 0.546
L 1868 0.288 1992907 0.338
Overall 11% of the world population (and yours truly) is left-handed and those of Hispanic lineage (which overlaps considerably with my population of Caribbean players) are less likely (9.1%) to be sinister (the Latin word for "left" is sinstre) than dextral ("just" or "right" in Latin). Of course that small difference doesn't explain the much larger difference you see in players from the Caribbean. Many people have pondered this question and it would seem that the cultural bias against lefties in the Caribbean is likely the largest contributing factor. Players forced to write right-handed are therefore more likely to become switch hitters when they start playing baseball. A lesser factor might be related to position bias where more Caribbeans gravitate to middle-infield positions which are traditionally manned by righties.
Following this line of reasoning J.C. offered that since Caribbean hitters more often hit with the platoon advantage they might walk less and hit with a higher average as a result.
In a different study I'm doing of platoon advantage I found that hitters with the platoon advantage do indeed walk less frequently (actually .0013 walks per plate appearance less) than do hitters when they don't have the platoon advantage. They also hit for a higher average (+.024) when they have the advantage. In that study, however, I didn't include switch hitters which is very relevant here.
Using the table above and estimating that 30% of the plate appearances in the majors are against left-handed pitching Caribbean hitters actually hit with the platoon advantage 50.4% of the time while non-Caribbean do so 51.6% of the time. The reason for this is that Caribbeans include 8.4% more "pure" right-handed hitters (with pure in quotes since doubtless many of those are lefties like my Dad who were forced to be right-handed and then never returned from the Dark Side). So it would appear that platoon advantage doesn't really explain the difference.