A Validation Method to Determine Missing Years of Birth in a Cohort Study of Shipyard Workers Using Social Security Number

Abstract

Objective: The objective of the study is to evaluate the generalizability and feasibility of a prediction method developed by Block et al (1983) to estimate missing age of workers by using their Social Security Numbers (SSNs).

Methods: Our study used a retrospective occupational cohort of about 15,000 workers from the Long Beach Naval Shipyard (1978 to 1985).

Results: Our results showed an 89.2% agreement (P < 0.0001) between the predicted and observed years of birth using Block's method. The correlation increased to 93.1% (P < 0.0001) after our modifications by removing workers with SSNs issued in U.S. territories. The method performed better in shipyard workers who obtained their SSNs after 1950.

Conclusion: Although the method is useful in imputing missing age, the accuracy is dependent on the year, age, and location of SSN issuance.

Figure 1

Outline of the Long Beach Naval Shipyard cohort (1978–1985) validation study of Block’s method to predict years of birth using Social Security Numbers. LBNS, Long Beach Naval Shipyard; RRB, Railroad Board; SSN, Social Security Number.

Figure 2

Relationships between predicted and observed years of birth in LBNS-VC workers (n = 6,980). A) unmodified Block’s method, B) Block’s method with modification II. Arrow is cluster of workers with U.S. territories-issued SSN