Levitas v. Christian, 454 Md. 233

Michael Christian had multiple elevated blood-lead or FEP tests between 1990–1993 while living at two Baltimore residences: 3605 Spaulding Ave (Spaulding) and 4946 Denmore Ave (Denmore).
In 2011 Christian sued Stewart Levitas, owner of Spaulding, alleging negligence and consumer-protection claims based on lead paint exposure; Arc Environmental testing in 2012 found numerous lead-positive interior surfaces at Spaulding.
Christian designated pediatrician Howard Klein, M.D., as an expert on (1) source causation (that Spaulding was a source of lead exposure) and (2) medical causation (lead caused cognitive injury and IQ loss, using the Lanphear study to quantify IQ loss).
Levitas moved to exclude Dr. Klein for lack of qualifications and insufficient factual basis; the circuit court excluded Klein’s testimony on source and medical causation and entered summary judgment for Levitas (to permit appeal).
The Court of Special Appeals reversed on remand; this Court granted certiorari to decide whether the trial court abused its discretion in excluding Klein’s testimony on (1) lead-source causation and (2) medical causation.

Issue	Plaintiff's Argument (Christian)	Defendant's Argument (Levitas)	Held
Admissibility of expert testimony on source causation (Spaulding as a source)	Klein was qualified and relied on multiple facts (Arc Report, DHCD/MDE records, contemporaneous elevated tests, family testimony, residence history) sufficient under Rule 5-702	Klein lacked an adequate factual basis because he did not exclude or sufficiently investigate other possible sources (Denmore and others)	Reversed circuit court: Klein admissible on source causation; trial court applied wrong standard by requiring exclusion of other properties and abused its discretion
Admissibility of expert testimony on medical causation (lead caused cognitive injury/IQ loss)	Klein (though he relied on Hurwitz’s neuropsych report and the Lanphear study) was qualified and had a sufficient factual basis; methodological disputes go to weight, not admissibility	Klein was unqualified to interpret IQ testing he did not administer and lacked factual basis because he did not examine the plaintiff and relied on population study to calculate individual IQ loss	Reversed circuit court: Klein admissible on medical causation; qualifications and reliance on Hurwitz and Lanphear are proper under Rule 5-702; deficiencies are for cross-examination and weight

Roy v. Dackman, 445 Md. 23 (2015) (expert admissibility requires adequate factual basis and methodology; distinguishing ‘rule in’ evidence from expert source causation)
Ross v. Housing Authority of Baltimore City, 430 Md. 648 (2013) (expert must explain how data were weighed; conclusory source opinions may confuse the jury)
Hamilton v. Kirson, 439 Md. 501 (2014) (discussion of ways plaintiffs may establish property as source; evidence of other sources does not automatically preclude liability)
Rodman v. Harold, 279 Md. 167 (1977) (expert need not have hands-on experience with every technique to be qualified)
Exxon Mobil Corp. v. Ford, 433 Md. 426 (2013) (expert opinion must be more than speculation; factual basis and reliable methodology required)
Pittway Corp. v. Collins, 409 Md. 218 (2009) (explains substantial-factor causation when multiple negligent acts may contribute to harm)