The problems and limitations of cohort studies

Summary

Chronic obstructive pulmonary disease (COPD) is the third most common cause of mortality worldwide and it is important to discover whether risk factors can be identified from studies undertaken in childhood.

Numerous longitudinal cohort studies have been developed in many parts of the world to better understand the long-term outcomes of chronic respiratory diseases. Using data they have generated, it should be possible to identify specific risk factors in children and develop a model to prioritise their importance when found, in order to consider ways to reduce the prevalence and/or severity of disease in adults. However, this does require the sharing of data within the field, as is happening in other related fields, such as the Virtual International Stroke Trial Archive (www.vista.gla.ac.uk). Pooling of the raw data could be very informative and an organisation such as the European Respiratory Society could play an important role in ensuring this happens.

Unfortunately, cohort studies vary widely in their inclusion criteria, their methodology and the format in which lung function data are presented. The raw data required to develop a model to assess the impact of childhood risk factors on future lung function have not been made available from many of the published articles.

Our initial belief that recognised risk factors are independent variables was naïve and a different approach is required to better understand their interdependence.