Hi alexandre soufan,
in the table overview create a field start_date and end_date. Then create relationship which says:
person_id = person_id AND
start_date <= date AND
end_date >= date
Through this relationship you can count no_analyses in selected interval
Thanks for the quick solution. It seems to work! One small thing though; each time I would like to check the number of analyses per person in a certain range, I would have to change the interval for each person. Is it possible to use a static variable for this so the range gets centralized, instead of two extra fields? Or could it be done using another table containing the date range?
Yu can set start_date and end_date as global fields