Adverse inference is a legal inference, adverse to the concerned party, drawn from silence or absence of requested evidence. It is part of evidence codes based on common law in various countries.
According to Lawvibe, "the 'adverse inference' can be quite damning at trial. Essentially, when plaintiffs try to present evidence on a point essential to their case and can’t because the document has been destroyed (by the defendant), the jury can infer that the evidence would have been adverse to (the defendant), and adopt the plaintiff’s reasonable interpretation of what the document would have said..." [1]
The United States Court of Appeals for the Eighth Circuit pointed out in 2004, in a case involving spoliation (destruction) of evidence, that "...the giving of an adverse inference instruction often terminates the litigation in that it is 'too difficult a hurdle' for the spoliating party to overcome. The court therefore concluded that the adverse inference instruction is an 'extreme' sanction that should 'not be given lightly'...". [2]
This rule applies not only to evidence which is destroyed, but also to evidence which exists but the party refuses to produce, and to evidence which the party has under his control, and which is not produced. See Notice to produce. This adverse inference is based upon the presumption that the party who controls the evidence would have produced it, if it had been supportive of his/her position.
It can also apply to a witness who is known to exist but which the party refuses to identify or produce.