Expert evidence. Opinion evidence such as "if a and b then in my view c will happen.
Factual: I saw him let it go and it fell to the floor.
Opinion: In my opinion the laws of gravity are such that if an object is released it will fall to the floor.
Strict rules of evidence. Judges, and in appropriate circumstances arbitrators, will accept the simplistic view of evidence given above. The strict rules of evidence may require more. Moreover evidence can be challenged and controverted but above all it has weight. If simplistic evidence is challenged successfully it has little weight. If three pieces of evidence collaborate a particular fact then that is strong evidence.
A difficulty for those presenting a case (especially their own) is that they may think that they have put up strong evidence but they have no idea how much weight it will be given by a Judge or Arbitrator in reaching his Judgement or Award. In arbitrations it is possible to find out what has been absorbed by the arbitrator if all parties agree to tell the arbitrator that he is to produce a "Report" on what he has found out before coming to his decision. It is not customary for arbitrators to produce such reports and they will require to be paid for producing them. On the other hand an arbitrator's report should be much less expensive than an expert's report because an arbitrator naturally expects to stand corrected - that's the purpose - while an expert has to ensure that every detail of his report will stand up to cross- examination in the witness box.
Factual witnesses should put in Witness Statements in advance of the hearing setting out what they have to say. Witness Statements are usually taken as being the evidence of a factual witness without them having to go through it in the witness box. The lawyers' jargon is "evidence-in-chief" and the witness will be cross-examined on it.A Witness Statement contains a Statement of Truth.
Expert Evidence from expert witnesses must always be made available to the court or arbitrator and the opposing parties a good time prior to the hearing in the form of a Report. Follow the link for examples. An experts report contains a Statement of Truth.
A Preliminary Meeting may be held or a conference telephone call set up to formulate Arbitrators Directions which will include covering timetabling of the Witness Statements and Experts Reports. Judges hold case management hearings with the same end in view.