*6.1. Association*

An association is a link between two items or variables. Sometimes the link may be coincidental or spurious and occur strictly by chance, and sometimes a link may be meaningful and occur with a higher probability than by chance alone. An example of a coincidental association is demonstrated by flipping a coin. The outcome of heads or tails is strictly a matter of chance, assuming you are using a fair coin. Even if turning up 99 heads in a row, the chance that the next coin flip will turn up tails does not increase; it still remains at approximately 50%. Betting that there is a meaningful association between the number of coin flips and the chances that heads or tails will turn up next is known as a gambler's fallacy [71].

**Figure 2.** Graphical abstract. Like a jigsaw puzzle, pieces of knowledge are synthesized to form a coherent picture of new knowledge.

When associating concepts in a synthesis, the aim is to form a relationship in which the variables are meaningfully associated—as one variable changes, the associated variable also changes to some degree, known as covariance. But this does not necessarily mean that one variable is causing the other to change. Let us say the average person gets two colds a year and also takes vitamin C supplements. You do not take vitamin C supplements, and you observe that you ge<sup>t</sup> more colds than the average person. You suspect that taking vitamin C supplements may be associated with a reduced number of colds per year. But even if you are able to confirm that these two variables are statistically associated, as claimed in advertising using results of a clinical study, you still may not know what is causing the association between the variables. Perhaps people who take vitamin supplements look after their overall health better than you, which could be a confounding factor that independently causes the same outcome of reduced colds; which brings us to the next section.
