"Goitre is prevalent in high altitudes"- is an example of:

The indirect association is an association between a characteristic (or variable) of interest and a disease due to the presence of another factor, known or unknown that is common to both the characteristic and the disease. This common factor is also known as the "confounding" variable. In the above example iodine deficiency is the confounding variable. High altitude Iodine deficiency Goitre prevalence Ref: Park 21st edition, page 85.