There are often diet and lifestyle similarities in groups or subgroups of individuals who develop disease. For example, researchers for some time of pointed out the correlation between the consumption of diet soda and obesity and have examined the link between the consumption of fatty foods and increased breast cancer risk. Blood sugar will rise in any case.
However, the correlations themselves do not provide evidence of causality and may or may not be a real contributor to the increased incidence of disease. Through time there have been myriads of investigations, often based upon a prospective analysis of an existing database, which identify a potential relationship between a particular factor and a specific condition or disease.
Although scientists are generally upfront regarding the limitations of their findings, media reports often fail to explain that a particular link is not necessarily indicative of a cause and effect relationship.
The many unobserved variables can lead investigators to identify fortuitous correlations between multiple factors and effects which are the product of something that is unknown or simply not considered. Despite considerable research, the cause of chronic fatigue syndrome remains unknown. However, correlations exist between the malady, viral infections, psychological stress and other immune disorders. Yet, no evidence exists which identifies any of these as causal.