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F1: fertility-rate predictor inconcistency between estimation and Java implementation

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Dal 23/10/2026.

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Descrizione

The UK F1 equation is estimated using a national annual fertility-rate series, but Java evaluates the coefficient using a regional measure derived from population projections. This mismatch remains in develop at commit 971d050, checked on 23 October 2026.

Estimation

The UID construction assigns dukfr by calendar year only, with the label "UK General fertility rate (ONS)": 02_create_UKHLS_variables.do, lines 1846–1867.

The regression preparation then sets fertilityRate = dukfr (variable_update.do, lines 679–680), and the active F1 probit includes fertilityRate. Thus all observations in the same year receive the same national rate, irrespective of region.

Java implementation

For ordinary simulated persons, the FertilityRate getter instead calls getFertilityRateByRegionYear(getRegion(), getYear()). The lower-case fertilityRate getter delegates to it (lines 4016–4018).

Parameters.java, lines 1932–1960 constructs this as the projected number of children aged zero in the region divided by the projected number of women between the maternity-age limits, currently 18–49 (constants). The getter multiplies this by 1,000.

The coefficient is therefore applied to a different predictor from the one used in estimation: both the geographical variation and the construction differ. This is not a missing per-1,000 conversion, and switching fertility alignment on or off does not make the two predictor definitions consistent. The size of the effect on validation results needs to be assessed after the intended definition is agreed.

Question and proposed resolution

Should F1 be re-estimated using a consistently defined regional fertility-rate series, as suggested in the meeting, or should Java instead use a national predictor consistent with estimation?

Would it make sense to agree on a common definition for estimation and simulation, including the geographical coverage, age range and timing? If this involves changing the predictor used in estimation, I imagine we would also need to re-estimate F1. I would be happy to help check the resulting consistency between Stata and Java.

Lingua principale
Java
Stelle
26
Fork
38
Merge medio
13h 5m
PR unite (30g)
7

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