text: Over the past 50 years , great efforts have been spent on gathering data across medical practice , hospital , provincial , state , and even country boundaries to study the interdependence of environmental and cultural factors on cancer incidence .
simplified: Over the past 50 years , great efforts have been made on collecting data across medical practice , hospital , provincial , state , and even country boundaries . This data is used to study the sharing dependence of environmental and cultural causes on cancer incidence .