Calculation of life tables from survey data: a technical note.

Area of Science:

• Demography
• Biostatistics
• Epidemiology

Background:

• Life table calculations often rely on survey data where exact event dates are unavailable.
• Dates are frequently coded in monthly intervals (e.g., century months), necessitating specific analytical approaches.
• Standard life table methods may not adequately account for the unequal duration of the initial exposure interval.

Purpose of the Study:

• To highlight the importance of adjusting life table calculations for the shorter first duration interval when using monthly data.
• To demonstrate how failure to account for this interval can introduce substantial bias in demographic estimates.
• To illustrate the impact of this methodological issue on the estimation of fecundability.

Main Methods:

• Utilized life table methodologies applied to survey data coded in monthly intervals.
• Compared standard calculations with adjusted calculations that account for the first interval's reduced length.
• Employed World Fertility Survey data from four countries to estimate fecundability.

Main Results:

• Failure to adjust for the first interval's half-length significantly biases estimates for events with high early-life frequency.
• Estimates of fecundability were shown to be substantially affected by this methodological oversight.
• The bias is non-trivial and can lead to inaccurate demographic inferences.

Conclusions:

• Accurate life table calculations from monthly data require explicit adjustment for the initial interval's duration.
• Demographic estimates, especially concerning fecundability, are vulnerable to bias if this adjustment is omitted.
• Methodological rigor in handling time intervals is crucial for reliable survey data analysis.