In more sequential terms, what transpires is that the analyst is called to the stand. The attorney who called this individual then proceeds with a line of questions designed to establish the qualifications (education, training, knowledge, skill, etc) that are sufficient for the court to accept them as an expert in their particular field. The attorney, at the conclusion of his qualifying questions then "proffers the witness" as an expert in the field. Prior to the court ruling, the judge will inquire whether the opposing counsel wishes to make an inquiry of the witness, which is known as "voir dire." This provides the opposing counsel an opportunity to challenge the qualifications and preclude the analyst from being accepted by the court as an expert.
If the court does not recognize the analyst as an expert in the particular field, then the analyst will not be permitted to give any opinion testimony. On the other hand, where an analyst is recognized by the court as an expert in a particular field, the analyst will be permitted to give opinion testimony evidence.
Attorneys (both prosecution and defense) may attempt a tactic where, after being recognized as an expert in a particular field, they attempt to elicit opinion testimony outside the range of their particular expertise. All attempts to solicit an opinion outside the scope of an analyst's expertise should be responded to with "I am unable to render an opinion in that field as I am not qualified as an expert in that particular area."
Witnesses must ensure that their curriculum vitae (CV) is accurate, complete, and free of any errors or omissions. Analysts should not underestimate opposing counsel checking into the background and representations of the witness on the CV.