Corroborating evidence (or corroboration) is evidence that supports a proposition already supported by initial evidence, therefore confirming the original proposition.

The polygraph examination results must, therefore, confirm initial/existing evidence.

In order to answer this question it is important to consider that the outcomes of disciplinary hearings and CCMA arbitrations are decided on a balance of probabilities.  The chairperson or CCMA commissioner must weigh up the evidence and decide whether the employer has proven that their allegation/charge is more probable than not.

There must be sufficient initial evidence that is corroborated by the polygraph examination result to meaningfully tip the scale in favour of the employer’s charge/allegation against the employee.

(In re H (Minors) [1996] AC 563 at 586), Lord Nicholls explained that it was a flexible test:

“The balance of probability standard means that a court is satisfied an event occurred if the court considers that, on the evidence, the occurrence of the event was more likely than not. When assessing the probabilities the court will have in mind as a factor, to whatever extent is appropriate in the particular case, that the more serious the allegation the less likely it is that the event occurred and, hence, the stronger should be the evidence before the court concludes that the allegation is established on the balance of probability. Fraud is usually less likely than negligence. Deliberate physical injury is usually less likely than accidental physical injury……… Built into the preponderance of probability standard is a generous degree of flexibility in respect of the seriousness of the allegation. Although the result is much the same, this does not mean that where a serious allegation is in issue the standard of proof required is higher. It means only that the inherent probability or improbability of an event is itself a matter to be taken into account when weighing the probabilities and deciding whether, on balance, the event occurred. The more improbable the event, the stronger must be the evidence that it did occur before, on the balance of probability, its occurrence will be established.“

Most investigative polygraph examinations in South Africa are conducted in pursuance of investigation into theft and fraud in the workplace. Theft and fraud are serious allegations and, using the above explanation, the probability that an employee committed theft or fraud will be considered to be theoretically lower at the outset than the probability that an employee swore at a colleague during an argument or lied about why they were late for work, for example.

Aside from understanding the concept of balance of probability it is also important for employers to ensure that all efforts are made to gather the necessary evidence to support their case. What may seem a “slam dunk” case to the unwitting employer may be anything but when the matter is scrutinised by a CCMA commissioner who always has a thorough knowledge of the legal requirements for proving a dismissal was procedurally fair and substantively fair on a balance of probabilities.