Question

Why do some answers on i-Base use different words for similar testing questions?

18 February 2008. Related: All topics, HIV testing.

Your service is great!! Thanks.

However, I have seen different answers by different people in response to similar questions. Some of you guys will say “definitely not infected” while others would say “safely assume not infected”.

Why the diiferent approach, when most of it is regarding testing after the window period?

Answer

Answer: Simon Collins

The quick answer for why some answers on the site use different words, is that each advocate brings their individual interpretation to each question.

Generally, because we focus on research, the answers should be the same, but the wording may differ.

The longer answer, especially relating to this example, is that, scientifically, it is not possible to ‘prove a negative’ – you cannot prove something has not happened. Being very careful with words means that, a scientist will rarely say something ‘can never happen’ just that is its ‘very unlikely’ or even ‘very very unlikely’. Or they may qualify it with a number such as one in a million – or one in 10 million etc.

With HIV test results, very occasionally, cases are reported when someone seroconverts outside the normal window period – perhaps 6 or 9 months after exposure. In practice this is so rare that a negative result after 3 months, confirmed at 6 months, is accepted as a negative result.

In the context of the questions we get – which are generally from worried people, who are often at very low or even zero risk of having caught HIV – the clearest message is that they should belive the results and they are negative.

Scientifically speaking – if you are being absolutely precise to never be proved wrong – then “safely assume not infected” is more accurate.