Follow our train of thought: we have posted about the misuse of the differential diagnosis concept, as plaintiff experts morph it from an accepted tool for deciding what is wrong with a patient to a method for explaining why and how the patient suffered his injury/illness.  Now, three computer experts sought to opine that a software flaw prevented a health monitor alarm from sounding, claiming their methodology was just “like a medical differential diagnosis”!  Fortunately, the South Carolina Supreme Court rejected that attempt last week.  See Graves v. CAS Medical Systems Inc., No. 27168 (S.C., 8/29/12).

Their doctor ordered that the plaintiffs use a monitor manufactured by CAS to track their infant child’s breathing and heart rates as a precaution. The monitor was designed to sound an alarm, if the subject were to experience an apneic, bradycardia, or tachycardia event. Once the breathing or heart rate returns to normal, the alarm stops. Each machine also keeps a log of any events, which is the term for when the alarm sounds, and records the pertinent data and vital signs. As an additional safety measure, CAS installed not only a back-up alarm, but also a feature that records whether the alarm sounded. This system operates primarily through an independent and separate microphone specifically designed to listen for the alarm. If it hears the alarm, it then makes a notation in the monitor’s internal log. If it does not hear the alarm, then it records “Front alarm not heard,” and the monitor will sound the backup alarm. A microphone listens for this back-up alarm as well and records whether it was heard. If the back-up alarm fails, all the lights on the front of the monitor flash.

Tragically, the child died from Sudden Infant Death Syndrome (SIDS), which essentially means that no attributable cause of death exists. Plaintiffs claimed the monitor’s alarm never sounded that night. Additionally, they testified that all the lights on the front of the monitor were on, although they were solid and not flashing. Another family member who was asleep downstairs also allegedly could not recall hearing the alarm go off.  Plaintiffs further testified the machine was not turned off until the next day, when the monitor was removed for testing.

Plaintiffs filed a strict liability design defect claim against CAS, contending the monitor’s software design caused the alarm to fail.  Their claim revolved around what is known as “spaghetti code,” which is when computer code is unstructured and can result from the overuse of “goto” or “unconditional branch” statements, which causes a signal working its way through the code to jump around instead of following a linear path.  This in turn caused the signal to be pushed off course and never reach its destination.

To support this theory, the Graves designated three software experts to testify regarding the alarm’s alleged failure. In arriving at their conclusions that a software defect caused the alarm to fail, none of the experts did much actual testing of the software. Instead, they used a “reasoning to the best inference” analysis, which was “similar to a differential diagnosis” in the medical field. In this case, three potential causes were identified: hardware error, complaint error, and software error. Complaint error means that the monitor was misused or the alarm did sound and the Graves failed to hear it.  All the experts were able to dismiss hardware error as a cause because the machine was tested and shown to be functioning properly. Thus, the question became whether complaint error or a software error occurred.

The experts excluded complaint error because the machine was hooked up properly, and they did not believe anyone would sleep through the alarm. In other words, because the Graves claimed the alarm did not wake them, that means it must not have gone off. After being confronted with the fact that the monitor listens for the alarm and separately records whether it was sounded, the experts opined that it must be “certain” the internal logs showing the alarm actually did sound were not reliable “in light of the undisputed testimony that the alarm did not function.” That left software error as the most likely cause of the alleged failure, they opined.

Defendant moved to have all these experts excluded, arguing none of them met the reliability factors for scientific testimony set forth in State v. Council, 335 S.C. 1, 515 S.E.2d 508 (1999). CAS also moved for summary judgment, contending that without this expert testimony plaintiffs had no evidence of a design defect. The trial court agreed that their opinions were unreliable both as scientific evidence and as nonscientific evidence and thus were inadmissible. Having excluded the opinions of all the Graves’ experts, the lower court granted CAS’s motion for summary judgment.

The state Supreme Court noted that this was its first opportunity to assess the reliability of an opinion rendered using the “reasoning to the best inference” methodology, so looked for guidance to the analysis of the United States Court of Appeals for the Tenth Circuit, which had already done so. In Bitler v. A.O. Smith Corp., 400 F.3d 1227 (10th Cir. 2004), the court held that “[e]xperts must provide objective reasons for eliminating alternative causes” when engaging in this analysis. Id. at 1237. Furthermore, “an inference to the best explanation for the cause of an accident must eliminate other possible sources as highly improbable, and must demonstrate that the cause identified is highly probable.” Id. at 1238. Although the expert need not categorically exclude all alternate causes, that does not relieve the expert of his burden to prove the alternate cause is at least highly improbable based on an objective analysis. See id. at 1237–38 & n.6. The court found this objectivity requirement consistent with the quality control element of State v. Council.

Here, there was evidence that the alarm worked properly and the plaintiffs failed to hear it. In addition to the monitor’s recordation of hearing the alarm sound, the family pediatrician testified he believed plaintiffs slept through it, the court noted. The doctor was aware of just how exhausted the parents were. Although the alarm is loud, if one is tired enough, he testified that it is possible to sleep through it. His opinion was bolstered by the fact that the machine seems to have worked just as it was supposed to and recorded the breathing issues perfectly. The log also seems to show the alarm managed to stimulate the baby into breathing normally at times.

This evidence does not mean that is exactly what happened.  But there was enough that an expert needed to take it into account.. Instead, the experts simply assumed the alarm did not sound and provided no reason for discounting the evidence to the contrary other than the assertion of the persons alleging a failure. Thus, they did not objectively discount the evidence of complaint error as required. See Clark v. Takata Corp., 192 F.3d 750, 757 (7th Cir. 1999) (“Simply put, an expert does not assist the trier of fact in determining whether a product failed if he starts his analysis based upon the assumption that the product failed (the very question that he was called upon to resolve), and thus, the court’s refusal to accept and give credence to [the expert’s] opinion was proper.”).

The trial court did not abuse its discretion in excluding the opinions, and summary judgment was warranted.