The problems and limitations of cohort studies

Abstract

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 nai¨ve
and a different approach is required to better understand their interdependence