External characteristics of poultry have been used as criteria of egg production for a number of years. Only within the last few years, however, have attempts been made actually to correlate mathematically certain definite morphological characteristics with egg production. Data also have been published recently, correlating certain physiological characters with egg production.
Knox, C. W. and Bittenbender, H. A.
"Correlation of physical measurements with egg production in white Plymouth Rock hens,"
Research Bulletin (Iowa Agriculture and Home Economics Experiment Station): Vol. 8
, Article 1.
Available at: https://lib.dr.iastate.edu/researchbulletin/vol8/iss103/1