Possible errors in the data?

We’ve started collecting our data and  just wanted to double check an issue with you. We’re entering the number of half day absences due to illness but doesn’t this introduce inaccuracies if we’re not clear as to whether the number equates to say 30 children taken ill in the middle of the day (30 sessions) or 15 children absent for a whole day (also 30 sessions). The first situation suggests a much worse ‘outbreak’ of something than the second.

Of course this is also assuming that significant amounts of the illness is in fact caused by flu and not sickness, unapproved holidays, tests etc.