RESEARCH QUARTERLY

leagues until they were quite old. In the latter case it would be possible
to make a simple, direct comparison of the average performance of each
successive age group. But, because selective factors operate so con-
stantly and so relentlessly, it is not possible to employ the foregoing
procedure. For this same reason the correlation technique is likewise
quite useless for the study of age differences. Indeed, careful analysis
of the available data reveals that the average proficiency of the several
age groups that participate in major league baseball does not differ
appreciably. This is due to the fact that the professional ball player
is not employed by the league management until he has exhibited a high
level of proficiency. And, as soon as a particular player falls below a
very high standard of excellence, he is released by the management
and no longer permitted to exhibit his lesser skill in the same class of
baseball competition.

Since players are not permitted to remain in the major leagues when
they fail to display very great skill, the writer has studied age differ-
ences in baseball proficiency by simply tabulating the ages of indi-
viduals whose names appeared in the successive annual editions of
Who’s Who in Baseball*® from 1916 to 1938 inclusive.*

In the foreword of Who’s Who in Baseball, the publishers make the
following explanatory statement:

This book, as its name implies, is devoted to the better known or more
talented players of the two major leagues. Who’s Who does not claim to
present the records of all the major league players nor even of all the regu-
lars. Such an attempt would be impossible, if for no other reason, because of
the continually changing personnel of the big clubs.

If the editors of Who’s Who in Baseball have succeeded in listing
the more talented players of the two major leagues, tabulation of the
ages of the players whose names are included each year should reveal
the chronological ages at which baseball players are maximally profi-
cient.+ What ate the chronological ages at which players most fre-
quently exhibit such a high degree of baseball skill as to warrant inclu-
sion of their names in Who’s Who in Baseball?

Figure 1 presents a composite picture of the ages of the most
talented major league players (other than pitcherst) for a period of
22 years. This figure sets forth data for 3,126 player-years. As here
used the term “‘player-year” posits merely one full year’s performance
in a major league club, plus inclusion of the player’s name in Who’s
Who in Baseball for the succeeding year.§ Since the names of some

*The issue of Who’s Who in Baseball for the year 1922 (if there was one) was not
available to the writer.

+ It seems safe to assume that, in making their annual selections, the publishers of
Who’s Who in Baseball did not exhibit prejudice for or against any particular age groups.

t+ Data are presented separately for baseball pitchers.

§ Each edition of Who’s Who in Baseball contains data for the previous year. It
was therefore necessary to make allowance for the fact that the individual’s playing