A 2009 Court of Appeals case ruled partition ratio variability evidence is admissible to defend clients against impairment charges under Vehicle Code Section 23152(a), forcing the California Supreme Court to address this long avoided issue. 

Rather than making a determination as to what constitutes a sufficient foundation to admit such evidence, however, the California Supreme Court left it up to the lower courts to resolve.  In making rulings on admissibility, the courts then are likely to be faced with numerous considerations including: unknown variables (drinking pattern, temperature, hematocrit level, atmospheric pressure, etc.), whether law enforcement can perform experiments on the defendant and, if so, what about the defendant who is a recovering alcoholic trying to remain sober?, whether under the age of 21 defendants will receive a fair trial given they cannot legally participate in scientific experiments and is there evidence by the People that a .08 percent or higher blood alcohol level establishes impairment?

Given the range of variables and replication impossibilities, it is likely only partition ratio variability evidence pertaining to the general population will be admitted in defending against impairment charges in DUI cases, while partition ratio variability evidence pertaining to the individual will be excluded.