OPPORTUNITIES FOR IMMIGRANTS 
solely upon any of the available series or analytic studies. How- 
ever, these valuable pioneer studies have been utilized in some of 
the subsequent comparisons, and have afforded many suggestions 
for the preparation of our special employment index. 
Index of Factory Employment, by Months, 1889-1923. 
The index of employment opportunity which is most extensively 
used in the subsequent chapters is an Index of Factory Employment, 
representing an estimate obtained by the synthesis of some of the 
employment and unemployment series mentioned in above para- 
graphs. This index covers the period from January 1, 1889, to 
December, 1923, by months. For 1889 to 1894 the estimate is 
based upon Massachusetts data; for 1895 to 1903, on statistics for 
Massachusetts and New Jersey; for 1904 to 1919, New York is 
added; and for the years subsequent to 1919, the New Jersey series 
ceases to be available and the index rests upon data for New York 
and Massachusetts alone. For the period subsequent to 1914 other 
employment series are available and are used to corroborate the 
evidence presented by the Index of Factory Employment. The 
methods used in welding the available fragmentary data into a 
continuous comparable index may be briefly summarized as follows: 
L The Census of Manufactures’ statistics of wage earners em- 
ployed in factories in the years 1899, 1904, 1909, 1914, 1919, 
and 1921, were adjusted for known variations in their com- 
prehensiveness, in order to make them as comparable as 
possible throughout the entire period. 
Estimates, by months, of the number employed in factories in 
each of the three States—Massachusetts, New Jersey, and 
New York—were made by using the Census data for the 
given State as basing points and interpolating between Census 
years by means of indexes constructed from the available employ- 
ment and unemployment (inverted) data for the given State. 
The separate State estimates of numbers employed were then 
added together to get a consolidated estimate for the groups, 
and from this estimate an index, withthe Javerage lfor 1914 = 
100, was computed, due allowance being made'for the changes 
in 1895, 1904, and 1920 in the number of States included 
The monthly figures for this Indez of Factory Employment, in 
terms of percentages of the 1914 average, are given in Table IVyin 
the Appendix, for the convenience of investigators who may wish 
69