Risk Communication Issues: Uncertainty

The concept of uncertainty holds different meanings for different individuals. For scientists, uncertainty is a quantifiable measure of the degree of confidence in a piece of information. Often, in science, findings are given in 95% confidence intervals, which means that the scientist is sure that the findings are accurate 95% of the time. Science does not often deal in guarantees, nor are things presented as being 100% certain.

This notion of quantifying the degree to which one is sure about something is not easily conveyed to or accepted by the public. The lay public does not measure uncertainty on a regular basis; something is usually known or not known.

Additionally, the way the burden of proof lies in science is often confusing. When chemicals are tested for their potential consequences on human health, a null hypothesis is employed, meaning that a chemical is assumed to have no effect until an effect can be statistically shown. Chemicals are, in essence, innocent until proven guilty of causing negative health effects. It is important to recognize, however, that the absence of evidence should not be taken as the evidence of absence. Scientists acknowledge that chemicals are not proven to be safe, only that they have not been shown to cause harm. This leaves ample room for uncertainty, and ample space for a non-scientist to have doubts about what the scientific evidence actually shows.