Another limitation is the reduced number of children with lead measurements, limiting interpretation of analyses controlling for lead exposure.
Some researchers attempt to control for lead time by comparing incidence up to 10 years above the upper age limit for screening [ 5].
Next, we evaluated associations between uric acid and six renal function outcomes, with and without control for lead, while adjusting for blood pressure and other covariates.
Kalager and colleagues [ 5], who used this method of controlling for lead time, observed an 18% excess incidence in the Norwegian breast screening program at approximately 10 years.
We supplemented the blood lead screening and airport location data with data from county tax assessor databases on age of housing (to control for lead exposure risks from deteriorating lead-based paint), resolved at the individual tax parcel level.
Similarly, the attempt by Kalager and colleagues [ 5] to control for lead time by comparing the screened population with subjects in the unscreened population who are 2 to 5 years older is inadequate for adjusting for lead time.
We also considered whether controlling for lead (log10-transformed), a known neurotoxicant, altered results for DAP concentrations in the subsamples with cord (n = 229) or 2-year (n = 296) lead values.
Higher hemoglobin was associated with an increase of 2.7 points of IQ among children with the wild-type alleles and was significant even after controlling for lead, midarm circumference, age, sex, parental education, family income, and number of children in the family unit (p < 0.0001).
We also controlled for lead-time bias in this analysis.
The impact of delay (defined as having symptoms for 12 or more weeks) on survival was measured from the date of diagnosis and from the date when the patient first noticed symptoms to control for lead-time bias.
