Research about the communication of risks has shown that the context and format in which risks are presented affect people's perception and their subsequent decision. Basically, three formats for communicating risk can be distinguished: verbal terms, a numerical format, and a graphical format. The use of verbal labels for communicating risks appears to be less effective in clearly explaining risks because people differ greatly in their interpretation of verbal labels. Although many people prefer to receive risk information in numbers, they find it difficult to understand these risks and use them for their decisions. Not much is known about how and even whether graphical risk information helps individuals to understand risk information. Individual perceptions of risk are assumed to play an important role in decisions, but people's perception is often inaccurate. In an attempt to make risks personally meaningful, people focus on the outcome of a risk and a numeric risk is translated into two broad categories: the event will either happen or it will not happen. This 'binary perception' of risks especially occurs when the outcome evokes emotions. Decisions about prenatal screening and other health decisions often involve emotions. This makes it even harder to clearly communicate risks to people.