References
- Green , H. W. 1939 . Economic status of families living in each of the census tracts . Sheet-A-Week , 7 ( No. 1 )
- Olson , W. C. and Hughes , B. O. 1940 . “ Subsequent growth of children with and without nursery-school experiences ” . In 39th Yearbook, Nat. Soc. Stud. Educ 237 – 244 .