[MUSIC] Now so far we've covered both the definition and calculations for Measures of Association. Next, let's learn how to correctly interpret the measures of association. Once you've learned these, you might actually find yourself critiquing news reports or discussions in the news that are incorrectly using the measures of association. After you have reviewed this segment you should be able to do the items listed in the learning objectives. These include interpreting the measures of association, and recognizing which measures of disease occurrence or frequency, and association are commonly used with different study designs. How do I know if an exposure has a positive or negative effect on the disease that I'm interested in? Or how do you know if the exposure doesn't have any effect at all? Here are the guidelines for relative measures of association i.e., ratios. If the risk rate is equal to one then there is no association between exposure and the disease or health outcome. If the risk ratio or rate ratio is greater than one then the risk in the exposed or rate in the exposed is greater than in the unexposed. If the risk ratio or rate ratio is less than one, then the risk in the exposed is lower than the unexposed. For absolute measures of association, i.e., differences, if the risk difference is equal to zero, then there is no association, i.e., the risk is the same in the both groups. If the risk difference is greater than zero, then the risk in the exposed is greater than in the unexposed. And if the risk difference is less than zero, then the risk in the exposed is less than in the unexposed. Note that the null value for differences is zero while for the ratios the null value is one. Let's preface the topic of which measures of association are commonly found with different types of study design by first noting that all the measures of association we have covered can be estimated in the cohort study design. However, some of the other study designs are not able to directly calculate risks and rates as you can in the cohort. So, here is a table illustrating the measures of association that can be commonly used for different types of study designs. Note that prevalence and odds ratios and differences are more commonly found with cross-sectional and case-control studies, while risk and rate ratios and differences are more commonly used with cohort studies. Risks and rate ratios cannot be directly calculated from case control and cross sectional studies. This concludes the segment on interpreting measures of association.