Association of Two variables explained by 3rd variable is ?

Ans. is 'b' i.e., Indirect association Association Descriptive studies help to suggest an aetiological hypothesis. Analytic and experimental studies test the hypothesis, derived from descriptive studies and confirm or refute the observed association between suspected causes and disease. Association may be defined as the concurrence of two variables more often than would be expected by chance. In other words, events are said to be associated when they occur more frequently togeher than one would expect by chance. Association can be of following types : - 1 .Spurious association Observed association between a disease and suspected factor is spurious, i.e., not real. In other words there is an observed association when none actually exists. 2.Indirect association The indirect association is a statistical association between a variable of interest and a disease due to the presence of another factor, known or unknown, that is common to both the variable and the disease. This third factor (i.e., the common factor) is also known as the confounding variable. For example, endemic goitre (disease) is found at high altitudes (variable), showing thereby an association between altitude and endemic goitre. But it is due to iodine deficiency which is common at high altitude. So, iodine deficiency acts as a confounding factor as it is associated with both high altitude and endemic goitre. 3.Direct (causal) association a) One to one causal relationship Two variables are stated to be causally related if change in one is followed by change in other. If It does not, then their relationship cannot be causal. b) Multifactorial causation The causal thinking is different in non-communicable disease (e.g., CHD) where the etiology is multifactorial, i.e., more than one factors are associated with disease causation.