Basis for Opinions

There is a variety of literature available to assist the expert witness in formulating a professional opinion. When offering opinion in a proceeding, the opposing counsel or party will challenge the expert to base that opinion on fact. Therefore, it is important to understand the type of materials available and how they may be of service to the expert in preparing to be a witness. Relevant literature review should include technical inserts or fact sheets provided by assay and/or instrument vendors, peer-reviewed journal articles about analysis, and interpretation of results as well as trade publications. The latter are useful for tracking trends and current issues such as specimen validity testing and cases of interest. Knowledge of assay limitations, cross-reactivity, and potential interferences is essential.

3.4.1. Case Reports and Controlled Studies

Oftentimes in forensic cases, case reports are crucial in determining the cause of death. Such reports are based on data for a single individual and provide information from a retrospective point of view. This is different from a controlled study, which can take a prospective or retrospective approach to generate statistically relevant data. A number of participants are recruited for carefully controlled experiments that attempt to identify current sociological and/or scientific patterns and trends.

Both documents can be equally important to a case, though in the forensic realm controlled studies may be few and far between. Case reports may be all an expert witness can rely on. A laboratory can test a newborn's meconium to determine if the mother abused drugs during pregnancy and provide a case report stating that fact, but it is obviously unlawful and unethical to conduct a controlled study on expecting women in hopes of quantifying the harm cocaine inflicts on fetuses in utero.

3.4.2. Peer-Reviewed and Non-Peer-Reviewed Documents

At one point or another during their career, many scientists publish their original work in peer-reviewed scientific journals. These publications are held in high esteem due to rigorous review and approval processes set in place by the editors and reviewers of the respective journal. Once the scientific findings are deemed sound by a panel of peers, the manuscript is accepted for publication. The processes alone are not enough to guarantee truth, but they do provide a strong foundation for labeling an author's work as valid.

When it comes to court proceedings, it is in the expert's best interests to rely exclusively on peer-reviewed works if possible over those lacking in similar checks and balances. While offers a wealth of information about a number of scientific topics, there are no safeguards to ensure that the information is credible.

However, it should not be written off as "junk science," either. A much broader body of work exists in non-peer-reviewed material, and such articles often reflect the current state of the science as seen through the eyes of the writer, usually an expert in the field. But when participating in a trial, the expert is providing testimony that will be used to sway the outcome, it is imperative the information provided be scientifically sound. A Note on Peer-Reviewed Works. When referring to a peer-reviewed work in court, the expert must be sure they are referencing the official results of a study and not the author's discussion of those results. While it is perfectly acceptable to agree with an expert's opinion, it is unacceptable to base an opinion entirely on somebody else's opinion.

3.4.3. Literature Totality

It is the duty of the expert to study literature from a variety of sources and weigh each piece against a common body of knowledge to ensure the concluding opinion formed is based in legitimate science. This is especially true when the expert testifies in court. In order for the expert's opinion to be taken seriously, the expert must be able to support it with articles and data that are held in high regard by expert's colleagues, peers, and discipline in general. In other words, if 20 studies were conducted on the harmful effects of propoxyphene and 19 of them reach the same conclusion, the expert must take that into consideration when forming their opinion, even if an attorney wants them to argue for the results of the single contradictory study.

3.4.4. Impeachment

Expressing an expert opinion in court is not always easy. Just as scientists are trained to manipulate molecules and chemicals, attorneys are trained to manipulate words. Opposing counsel will do its best to confuse the expert witness with clever rephrasing and added emphasis. They will put words in the expert's mouth and compare current statements to testimony provided 10 years ago.

In these situations, comprehensive experience is the saving grace of an expert. Expert opinion is based on the totality of expertise. Data can be wrong, articles can be wrong, but expert opinion can never be wrong. Opposing counsel should be reminded that expert opinion is based on materials provided to the witness about the case. If that material includes inaccurate or incomplete information, it will obviously affect the expert's opinion. If new facts are presented, the expert is well within their rights to request time to examine the evidence and re-evaluate their stance.

3.5. Pre-Trial Documents for Experts in Forensic Testing

The job of an expert witness begins before the person even appears in a courtroom, as they prepare and review paperwork that will be entered into evidence. Here are just some of the activities in which an expert may be asked to participate.

3.5.1. Written Reports

An expert may be asked to prepare written reports of his or her opinions, which may be useful in settling a case in lieu of going to trial. In it, the expert will explain his or her credentials and experience as it relates to the case and summarize significant facts that contributed to the forming of expert opinion regarding the case. Official documents that relate to their training and the specifics of the case should also be included, including but not limited to a CV for the expert witness, police and autopsy reports, depositions, test results, and letters and e-mails divulging important updates or developments.

It is important to find out whether or not the opposing party has an expert witness and if that witness has prepared a written report. If the answer is yes, the expert should request a copy and allow plenty of time to analyze it prior to submitting his or her own report (if possible), or before the start of the trial or hearing. Anticipation of possible questions or issues that might be raised during the hearing is also useful in preparation. The attorney or employer representative may have information in that regard that might assist the expert witness.

In addition, it is common to be asked questions about test reliability and accuracy and possible human errors leading to erroneous results. These questions are not always easy to answer; while the testing process is reliable, one cannot ensure that no one will ever make an error. When an expert witness formulates answers to these questions, it is important to keep in mind the difference between what is possible (anything) versus what is likely or probable. Multiple tests on separate aliquots are performed to minimize the possibility of error. As is true in any proceeding, the opinions rendered by the expert witness should be based on facts and scientific evidence rather than conjecture or anecdotal information.

3.5.2. Discovery Depositions

Often ordered by the opposing counsel, a discovery deposition is designed to present both sides of a dispute with the information that will be presented in a trial, thus eliminating the potential for any Perry Mason-like surprises. Depositions are taken under oath, generally in the presence of both attorneys and a court reporter and should be prepared for in the same manner that one prepares for court. If an expert witness is called to give a deposition, the person should be sure to bring any documents in his or her possession that relate to the case.

3.5.3. Affidavits

An affidavit is a written statement of the facts that is confirmed under oath or by affirmation and is used to document the personal observations, recollections, and actions but not opinions or expert witnesses. It may be executed before a person such as a notary public and can often be used in lieu of courtroom testimony. There are many types of affidavits, one of the most common being the "custodian of records" affidavit, in which the executor acknowledges to being the custodian of the physical evidence (such as a blood or urine specimen) in question.

3.5.4. Written Interrogatories

Written interrogatories are the written equivalent of discovery depositions, as both features a series of questions presented by opposing council. In this instance, however, the attorney is the author and will rely on the written report from the witness to answer questions relating to experience and opinion of the witness. The witness may be asked to review the document before it is submitted to the court.

3.5.5. Subpoenas and Subpoena Duces Tecum

Subpoenas are official summons issued by the court and provides notification that the expert is expected to appear in court. It includes general information about the case, when and where the expert will testify, and the contact information of the attorneys who requested the subpoena. Experts are often presented with an additional subpoena called the subpoena duces tecum, which requires the witness to produce the documents that support the expert opinion. Failure to respond to a subpoena is considered contempt of court. If an expert is unable to testify on the date or time indicated, the expert must contact the counsel and the court immediately to inquire about rescheduling. Failure to comply without the court's approval may result in fines, community service, or even a warrant for arrest.

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