What is the test for instructing a jury on adverse inference?

In Buksh v. Miles, 2008 BCCA 318, the court concluded that there is a threshold question that must be addressed before a judge sitting with a jury instructs a jury on adverse inference. The threshold question, which applies equally to a judge sitting without a jury, can be stated from para. 35 as: 1. the evidence that has been tendered; 2. any explanation for the failure to call the witness whose absence is cited as the reason for the adverse inference; 3. the nature of the evidence the absent witness might be expected to give; 4. the extent of any disclosure of an absent physician’s clinical records; and 5. circumstances of the trial, such as any agreement as to records relating to the absent witness that work contrary to the inference or reliance on records of the absent witness by a witness whose evidence has been tendered.