The overall risk of a product (or any one aspect of it) may be assessed qualitatively or quantitatively, but either way there are usually multiple factors to take into consideration. Combining these requires subjective judgements. In any situation where a risk assessment is needed to inform real legal, political or commercial decisions the type of assessment to be used will be severely limited by:

• - what data is available,
• - defects in that data,
• - the practical options open to the decision makers 

and how severe - or negligible - the magnitude of  risk would need to be in order to make any difference to the choice (that would otherwise be made) between practical options.