Table 5.

Challenges and recommendations

	Challenge	Recommendations
Study population	Dealing with participation bias	• Keep non-response or loss to follow-up to a minimum
	• Responders and non-responders	• Characterize non-responders or those lost to follow-up
	• articipants and non-participants	• Control for extent and direction of bias in final data analysis
	• Different types of participants
	• Participants lost to follow-up for the clinical assessment Finding an adequately sized and well-matched control group	• In case the number of controls is insufficient: incorporate other types of control subjects
		• Choose types of controls that are representative of the study population
		• Characterize and control for differences between survivors and controls
		• Compare self-reported data with an more objective source, such as medical records or registries
Data collection	Validating instruments for data collection	• Conduct reliability studies to account for inter- and intra- observer variation
		• If possible, use data collection instruments that allow for one investigator to analyse collected data (observer bias)