To fully appreciate the meaning of this phrase “Expert Opinion” let us define the words ‘Opinion’ and ‘Expert’ independently and Jointly. Black’s law dictionary 8th Edition defines  “Expert” as one who is skilled in any particular art or trade, profession being professed of particular knowledge, concerning the same. And if a person has acquired any special experience or special training in a particular subject to which court enquiry relates, such a person can be considered as an expert.

Also An expert is said to be one who has made the subject upon which he speaks a matter of particular study; practice or observation and he must have a special knowledge of the subject. Any person who has the experience to give an informed opinion on a matter outside the experience of Court is an Expert.

On the other “Opinion” is an estimation, a belief or assessment, a view held as probable, what one thinks about a particular question or topic, an assessment short of grounds of proofs, a formal statement of reasons for the judgment, a formal statement of professional advice.

To Merriam Webster dictionary  Opinion means a belief, judgment, or way of thinking about something : what someone thinks about a particular thing. Or an  advice from someone with special knowledge e. g an advice from an expert. Now let us join the words.

Opinion of Expert simply means  an opinion, which is given by a person who is an expert in a particular field. It may be in science, art, law or any other technical field. On a bare reading of section 68 of the evidence Act as amended which provides as follows;
“When the court has to form an opinion upon a point of foreign law, customary law or custom, or of science or art, or as to identity of handwriting or finger impressions, the opinions upon that point of persons specially skilled in such foreign law, customary law or custom, or science or art, or in questions as to identity of handwriting or finger impressions, are admissible.
(2) Persons so specially skilled as mentioned in sub – section (1) of this section are called experts”.
We can see that scheme of section 68  has stressed on different types of experts like foreign law, science, art, fingerprints, handwriting etc  and for one to be an expert he needs to be knowledgeable in his field of profession see the case of SHULUWA AND ANOR VS AYE AND ORS (2015) LPELR-40476 (CA).  
“An expert witness must be versed in a subject in dispute. His dexterity and knowledge in a subject must be special in the sense of being superlative.”Per OGBUINYA, J.C.A.
To be appointed as expert one must have attainment in professional qualification. Some professional experience or should have made special study in the subject. He must prove himself as an expert before the Court. Some training must have been practiced by expert into that scientific field or has special knowledge of that field. Or, if he has made some observations in that field. Opinion is sought so that the court is able to assess evidence with a reasonable degree by relying on its own experience. But in some cases the Court is not able to come to a conclusion on the basis of its experience because the Court is ill equipped. And for that, the opinion of an expert is being sought.

The opinion of an expert is said to be needed where the fact in issue becomes strange or out of the knowledge of the court in the case of A.C.N. v. Nyako (2013) ALL FWLR(Pt.686) page 424 at 462 Paras E-G on this proposition of law held as follows:
 “Where a Court or Tribunal is required to form an opinion upon a point, specified thereunder, the opinion of persons specially skilled in the areas are admissible. It is a condition precedent to the admissibility of the opinion tendered to enable the Court form its own opinion that it is that of a person specially skilled in the area the Court or Tribunal is required to form its opinion on a point. The qualification, experience and depth of the person’s learning are invariably the criteria which entitle him to tender his opinion in order to aid the Court or Tribunal. The person so qualified under the section is called an expert. His opinion is necessary and so admissible because same is outside the experience and knowledge of the judge as a judge of fact. It is the Court’s prerogative to determine that the person being called as a witness, by his qualification and learning on the subject in which the Court requires his opinion and the reasons for the opinion, is indeed specially skilled”. See also the case of Dagayya v. State (2006) ALL FWLR (Pt.308) 1212 at 1231.
The experts could be categorized into two, firstly, The Testifying expert; If the witness needs to testify in court, the privilege is no longer protected. The expert witness’s identity and nearly all documents used to prepare the testimony will become discoverable. Usually an experienced lawyer will advise the expert not to take notes on documents because all of the notes will be available to the other party. 
Secondly, Non-testifying experts; In the U.S., a party may hire experts to help them evaluate a given case. For example, a car maker may hire an experienced mechanic to decide if its cars were built to specification. This kind of expert opinion will be protected from discovery by the opposing party. In other words, if the expert finds evidence against their client, the opposite party will not automatically gain access to it. This privilege is similar to the work-product doctrine (not to be confused with attorney–client privilege). The non-testifying expert can be present at the trial or hearing to aid the attorney in asking questions of other expert witnesses. Unlike a testifying expert, a non-testifying expert can be easily withdrawn from a case. It is also possible to change a non-testifying expert to a testifying expert before the expert disclosure date.
expert opinion are admissible only when it becomes necessary for court to rely upon such opinion as decided in the case of In the case of Attorney General of the Federation v. Abubakar (2007) ALL FWLR 1264 at 1300 , the Supreme Court held :
“It has been said that the opinion of an expert is always necessary where he (the expert) can furnish the court with scientific or other information of a technical nature that is very much or even likely to be outside the experience and knowledge of the judge.    See Seismograph Services Nigeria Ltd. v. Ogbeni (1976) ALL N.L.R. 163.”
Nevertheless the court is at liberty to accept or the reject such opinion because they are not bound  by such opinions see the case of SHULUWA AND ANOR VS AYE AND ORS (2015) LPELR-40476 (CA).  
“It can be garnered from this clear provision that it is the Court that decides whether or not a witness is an expert, in the areas chronicled in the provision, using his knowledge and skill as the a yardstick. A Court is not bound to accept the evidence of an expert”.              
See also the cases of  Seismograph Services Ltd. v. Onokpasa (1972) 4 SC 123; Seismograph Services Ltd. v. Ogbeni (1974) 4SC 85; Oruwari v. Osler (2013) 5 NWLR (Pt. 1348) 535; Oando (Nig.) Plc. v. Adijere (W/A) Ltd. (2013) l5 NWLR (Pt. 1377) 37a; Akeredolu v. Mimiko (2014) l NWLR (Pt. 13881 aO7; Gundiri v. Nyako (2014) 2 NWLR (Pt.1391) 2L1; Rabiu v. Amadu (2013) 2 NWLR (pt. 1337) 36.
Moreover, for an expert opinion to be accepted in court certain conditions must be fulfilled as laid down in  OTUNBA F. E. SOWEMIMO ANOR VS. THE STATE (2004) 11 NWLR PT 885 P. 515 @ 532, Tobi JSC, referred to the case of WAMBAI V KANO NATIVE AUTHORITY (1965) NWLR 15, where it was held that:
“In certain cases, the evidence of opinion of an expert is relevant, but he must be called as a witness. He must also state subject in which he is to give his opinion and he must state clearly the reasons for his opinion.”
Also In the case of Attorney-General of Oyo State & Anor v. Fairlakes Hotels Limited & Anor (No. 2) (1989) NWLR (Pt. 121) 255; (1988) 12 S.C.(Pt. I) my Lord UWAIS, J.S.C (AHTW) stated that:
“It therefore follows that it is not sufficient to say that where a document written by an expert is tendered in evidence and that document or the testimony through which it is tendered, if unchallenged, then it must be acted upon. The document is certainly subject to scrutiny by the trial Court and its contents could, in the process of the scrutiny, be rejected if there is reason to do so, as was done in the present case by the learned trial Judge.” Per DONGBAN-MENSEM, J.C.A. 
It is  my humble opinion  that the court needs to  stress on professional qualification of experts and not exclusively on experience. Some guidelines should be made to ensure the reliability of expert’s opinion, his knowledge, experience, and qualification in that field in order to be termed as an expert for justice to be achieved.  Also It is the duty of the court not to occupy the role of an expert by themselves. it has always deprecated the courts to take the role of an expert.

The courts also has to verify the premises of the expert in one case and value the opinion in the other case when the direct evidence is well corroborated by the circumstantial evidence and conforms to probabilities, there is no reason why it should not be accepted. The mere fact that the expert has come to a different conclusion on a particular point would not render that part of his story open to doubt especially when the data on which the expert has come to that conclusion is insufficient. The data on which the expert weigh must weigh with the Court and the opinion of the expert must be judged in the light thereof. 
About the author
SHAMSUDDEEN AHMAD ChMC (S. A YOLA) is a student of faculty of law, Ahmadu Bello University Zaria. He can be contacted via [email protected] 
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