Hypothesis and Predictions – The Scientific Method in Claims and Litigation
Wednesday, September 20, 2023
by: Wade Lanning, Ph.D., Senior Engineer, ARCCA Inc.

Section: Summer 2023

The collaboration between an attorney and an investigator comes with challenges, particularly when it comes to communication between experts and non-experts. As an engineer, I find that one of the most common challenges that non-engineer clients face is in asking questions that I can use to set up an engineering analysis. Ideally, an experienced expert can help their clients select technically sound, feasible, and relevant analyses for the expert to perform. But, attorneys can use the scientific method to help them ask the right expert the right questions.
The scientific method can be presented in different ways, but it typically takes the form of the following steps:
  • Question – raised by the claims
  • Hypothesis – one or more possible answers to questions
  • Prediction – if X hypothesis is true, we would expect to see Y evidence
  • Experiment – gather real-world evidence to test the predictions
  • Analysis – use the evidence to see which hypothesis survive and might be true
Ideally, an experienced expert can use context provided by their client to take a question, then develop the rest of the analysis. However, an attorney who understands the scientific method can accelerate the process – or help out an expert less experienced in litigation matters – by developing hypotheses and predictions. By understanding and using the scientific method, an attorney can keep their expert on-target, avoid surprises, and keep expert fees under control.

Example: Tie Rod Failure

After a collision, a driver claimed that the collision occurred because they lost control of the vehicle due to a mechanical failure. Afterward, it was found that one of the vehicle’s tie rods had fractured. Since the tie rod was part of the steering system, this seemed to fit with the driver’s account that they lost control due to a mechanical malfunction.

Figure 1: A fractured tie rod that allegedly caused a collision.

The driver’s claim, if true, offered the driver a defense from other parties affected by the collision. The fractured tie rod could potentially support a claim against the shops that had worked on the vehicle, the vehicle manufacturer, the part manufacturer, and the municipality that maintained the road as potential defendants who might have caused the tie rod to fail, in turn causing the collision. This might prompt any of the potential defense attorneys to retain an engineering expert and ask the question: How did the tie rod actually fail?

The expert might reply: The tie rod was not just fractured, it was deformed (bent). In order for enough stress to be applied to the tie rod material and cause it to bend, the tie rod must have been intact when the bend was created. Thus, the deformation occurred first, followed by the fracture. This is useful information, but does not really speak to the core issue of whether or not the tie rod could have caused the collision.

Figure 2: The tie rod deformed (bent) before it fractured.

If, instead of asking a question, the attorney asked their expert to analyze two competing hypotheses, they would get a more on-target analysis. Or, an experienced litigation expert would recognize that they needed to develop these hypotheses based on the plaintiff’s claims:
  • The failure occurred due to forces from normal operation.
  • The failure occurred due to forces from the collision.
Given these hypotheses, engineering experts can provide a more useful analysis. If the tie rod failed by normal use, then it must have failed by either tension (pulling apart) or compression (squeezing together) – the only loading modes that it would experience as it pushed and pulled on the steering knuckle during normal service. The failure we saw was not consistent with tension, which could produce fracture, but not bending. But the failure could have occurred due to buckling in compression – which would result in some bending. Alternatively, if the tie rod failed due to the collision, it could have experienced an abnormal loading mode like three-point bending from contact with another object.

Giving our engineering expert hypotheses to compare set them up to apply the scientific method: They performed calculations to predict the force required to induce buckling or to induce bending in the tie rod. Then, in their analysis, the engineer compared these predictions to the way the tie rod actually failed, as if the forensic evidence was the result of an experiment.

Figure 3: The predicted strength of the tie rod in buckling was greater than the strength of the tie rod connection to the steering knuckle.

The engineer completed their calculations and predicted that buckling failure would require orders of magnitude more force than bending. Importantly, buckling would require so much force that the connection between the tie rod and the steering knuckle would also fail. On the other hand, bending would result in too little force to damage the steering knuckle connection. Because the steering knuckle remained intact, the engineer could safely eliminate the buckling hypothesis and rule out the scenario where the tie rod failure preceded the collision. Our engineer concluded that bending and fracture of the tie rod most likely resulted from the collision.

Formulating Hypotheses

The tie rod example illustrates how an attorney who participates in developing hypotheses and predictions can help set up their expert to provide useful and relevant analysis. Multiple hypotheses and their associated predictions can be assessed in parallel, or a single claim can be converted to a single hypothesis. In either case, the scientific method works by process of elimination. Hypotheses are revised or ruled out based on discrepancies between predictions and evidence. Hypotheses can survive elimination to become the best and most likely answers to a question.

Attorneys can make efficient use of experts by providing them with specific hypotheses to test, rather than open-ended questions. These hypotheses could be based on their own theories and/or on the opposing sides’ claims, keeping in mind that the scientific method functions by process of elimination. By understanding the scientific method, attorneys can get more utility out of their experts’ specialized technical knowledge.
Here are some additional hypotheses and predictions from real-world cases. Note that each hypothesis sets up predictions which can be tested, and possibly eliminated, in an experiment and/or examination of the available evidence:
  • Claim: Dead animal in a beverage can.
    • Hypothesis: The animal entered a beverage can during the canning process.
    • Prediction: An animal subjected to the subject beverage’s pasteurization and canning steps would come out of the can looking like the plaintiff’s photos.
  • Claim: A defective tool fractured and hurt a worker.
    • Hypothesis: The tool was manufactured such that is was too weak to safely serve its intended purpose or foreseeable misuse.
    • Prediction: If we test the strength of an exemplar tool, it will be lower than acceptable and fail in the same manner as the subject tool.
  • Claim: A defective pressurized system exploded and hurt a worker.
    • Hypothesis: The system failed due to a manufacturing defect.
    • Prediction: The part that failed had design and materials consistent with the parts made by the defendant manufacturer.
  • Claim: A fire was caused by a defective electrical appliance.
    • Hypothesis: The appliance was in its as-manufactured condition with all original parts.
    • Prediction: No evidence of replacement, third-party parts will be present in the remains of the device.
  • Claim: Injuries from a low-speed automotive accident.
    • Hypothesis: The forces exerted on the plaintiff’s body damaged materials in their body: cartilage, ligaments, tendons, etc.
    • Prediction: The forces in the accident exceeded were greater than what they experienced during their other reported activities like playing basketball and skiing.
  • Claim: A low-speed collision caused an engine/transmission failure.
    • Hypothesis: A collision that caused minor body damage to a vehicle also caused engine/transmission failure.
    • Prediction: Forces involved in the collision exceeded forces involved in normal driving.

Dr. Lanning is a Senior Engineer at ARCCA specializing in the forensic analysis of mechanical failures and material degradation, such as fracture surface analysis, metal corrosion, polymer oxidation and degradation, weld and fastener failures and plumbing system material failures. He also investigates consumer product failures (design or manufacturing defects, operator error) and accidents involving industrial equipment, as well as performing laboratory analyses of material composition, structure, and properties. Dr. Lanning is also experienced in cases involving industrial and laboratory safety, machine design and safeguarding, and manufacturing and material processing (such as tracing defects and damage to conditions in production, distribution, or service life and shipping damage, corrosion, coating defects, surface scratches, surface contamination, foreign objects in food/beverage containers, etc.)