A stronger conelation exists in blood concentrations in identifying recent exposure, but back-extrapolation
of last cannabis usage predicted from blood concentrations is compromised by factors such as frequency of usage and interpersonal PK.
These studies used back-extrapolation, historically available large-size particle data, or physical or chemical models complemented by visibility, emission, meteorology, and satellite data (Beelen et al.
Other studies in Europe and Canada predicted annual averages of nitrogen dioxide (N[O.sub.2]), nitrogen oxides (N[O.sub.X]), and [PM.sub.2.5] by back-extrapolation (Beelen et al.
Back-extrapolation of estimates of exposure from current land-use regression models.
Development and back-extrapolation of N[O.sub.2] land use regression models for historic exposure assessment in Great Britain.
The other expert, an environmental consultant, used subtraction methodology and back-extrapolation
Although the first measured COHb level in the patient described in this report was 23.3%, based on back-extrapolation
(using the half lives of COHb in 100% oxygen and in room air conditions), the patient's estimated COHb probably exceeded 40% at the end of her exposure, which is consistent with her reported symptoms.
In a sensitivity analysis, the modeled N[O.sub.x] values were rescaled using back-extrapolation to better correspond to the levels seen at the start of the follow-up period in this study (1993-1995).
The back-extrapolation was performed using information about the estimated total amount of traffic for each year and national vehicle fleet emission factors for Sweden based on the Artemis model (Sjodin et al.
When rescaling the exposure with back-extrapolation, the quartile limits were 19, 35, and 54 [micro]g/[m.sup.3] for the 2nd, 3rd, and 4th quartiles, respectively.
2000), necessitating a back-extrapolation from the measured concentration on the sampling date to earlier values assuming a 7.5-year elimination half-life for TCDD.
Because the back-extrapolations ranged over periods of 15-37 years, Aylward et al.'s (1996) back-extrapolated values were between [2.sup.(15/7.5)] = 4 and [2.sup.(37/7.5)] = 30.6 times larger than the measured serum levels, whereas Steenland et al.'s (2001) back-extrapolated values were between only 2r = 3.3 and [2.sup.(37/8.7)] = 19.1 times larger, that is, about 18-38% smaller than Aylward et al.'s values.