Baseline Subtraction Changed What the THC Model’s Concentration Curves Represented
The modeling study subtracted each participant’s baseline blood THC before analysis. Its plotted post-inhalation curves therefore represented increments over baseline, rather than unadjusted total concentrations.
Pre-existing THC was handled explicitly
Participants were asked to abstain before the session, but recent abstinence does not guarantee a zero starting concentration in every regular user. The investigators measured a baseline sample and removed that value from later concentrations before pharmacokinetic fitting.
An increment and a total answer different questions
Subtracting baseline helps focus on the witnessed session under a simplifying assumption about the background contribution. A resulting curve should not be described as the raw blood result that a laboratory would report at the same moment. Adding the baseline back also does not resolve all possible changes in residual THC over time.
Retain preprocessing when comparing studies
A baseline-adjusted exposure estimate cannot be compared blindly with an unadjusted concentration from another protocol. The subtraction did not demonstrate that residual THC caused no effects or that a person’s baseline concentration represented impairment. It was an analytical modeling step. Reports using these data should identify whether the quoted value is observed total THC, an adjusted increment or a model prediction before drawing conclusions about dose or functional condition.
Related analysis: the study’s broader findings and limitations.
