Why is Odds Ratio and Prevalence Ratio Estimates Different in the US?
Introduction:
In epidemiology and biostatistics, odds ratio (OR) and prevalence ratio (PR) are widely used measures to assess the association between an exposure and an outcome. While both ratios provide valuable insights into the strength of the relationship, they differ in their interpretation and estimation. This review aims to explore the reasons behind the differences in odds ratio and prevalence ratio estimates in the context of the United States.
Understanding Odds Ratio and Prevalence Ratio:
Before delving into the disparities, let's first establish a clear comprehension of odds ratio and prevalence ratio. Odds ratio pertains to the odds of an outcome occurring in the exposed group relative to the odds of it occurring in the unexposed group. It is commonly used in case-control studies and logistic regression analysis. On the other hand, prevalence ratio represents the ratio of the prevalence of an outcome in the exposed group to the prevalence of the same outcome in the unexposed group. Prevalence ratio is typically employed in cross-sectional studies and cohort studies, especially when the outcome is common.
Differences in Estimation:
1. Study Design:
One primary reason for the differences in odds ratio and prevalence ratio estimates is the variation in study designs
What is the difference between odds ratio and prevalence ratio?
Odds ratio (OR) and risk ratio (RR) are two commonly used measures of association reported in research studies. In cross-sectional studies, the odds ratio is also referred to as the prevalence odds ratio (POR) when prevalent cases are included, and, instead of the RR, the prevalence ratio (PR) is calculated.
How do you know when to use odds ratio?
When is it used? Odds ratios are used to compare the relative odds of the occurrence of the outcome of interest (e.g. disease or disorder), given exposure to the variable of interest (e.g. health characteristic, aspect of medical history).
What is the difference between odds ratio and incidence ratio?
The normally used odds ratio from a classical case-control study measures the association between genotype and being diseased. In comparison, under incidence density sampling, the incidence rate ratio measures the association between genotype and becoming diseased.
Why use prevalence ratio in cross-sectional study?
Since cross-sectional studies are particularly useful for investigating chronic diseases (e.g. prevalence of AIDS) where the onset of disease is difficult to determine, or for studying long lasting risk factors (such as smoking, hypertension, and high fat diets), the prevalence odds ratio will generally be the ...
What is an example of a prevalence ratio?
Prevalence of wheezing and coughing among smokers = 13/26=0.50. Prevalence of wheezing and coughing among non-smokers = 2/74=0.027.
Should I use risk ratio or odds ratio?
“Risk” refers to the probability of occurrence of an event or outcome. Statistically, risk = chance of the outcome of interest/all possible outcomes. The term “odds” is often used instead of risk. “Odds” refers to the probability of occurrence of an event/probability of the event not occurring.
Frequently Asked Questions
How do you interpret prevalence ratio less than 1?
A risk ratio or rate ratio of less than 1.0 indicates a negative association between the exposure and outcome in the exposed group compared to the unexposed group. In this case, the exposure provides a protective effect.
What is the difference between prevalence and risk?
In this analogy, prevalence is the proportion of the tub (the total population) filled with any water (prevalent cases and incident cases). Risk is the proportion of the tub filled with new, flowing water (incident cases). Rate is a measure of how quickly the water flows into the tub.
What does an odds ratio of 2.5 mean?
For example, OR = 2.50 could be interpreted as the first group having “150% greater odds than” or “2.5 times the odds of” the second group.
When should you not use odds ratio?
Unfortunately, there is a recognised problem that odds ratios do not approximate well to the relative risk when the initial risk (that is, the prevalence of the outcome of interest) is high. Thus there is a danger that if odds ratios are interpreted as though they were relative risks then they may mislead.
FAQ
- How do you calculate odds ratio in epidemiology?
- In a 2-by-2 table with cells a, b, c, and d (see figure), the odds ratio is odds of the event in the exposure group (a/b) divided by the odds of the event in the control or non-exposure group (c/d). Thus the odds ratio is (a/b) / (c/d) which simplifies to ad/bc.
- Do I use odds ratio or relative risk?
- Odds ratios (OR) are commonly reported in the medical literature as the measure of association between exposure and outcome. However, it is relative risk that people more intuitively understand as a measure of association. Relative risk can be directly determined in a cohort study by calculating a risk ratio (RR).
- Is prevalence ratio the same as risk ratio?
- The prevalence ratio (PR) is analogous to the risk ratio (RR) of cohort studies. The denominators for both ratios are fixed populations – fixed at the start of the study in the case of a cohort study, and fixed at the point or period of time for the case-control study.
What is "prevalence odds ratio"
What does odds of disease mean? | Odds ratios are used to compare the relative odds of the occurrence of the outcome of interest (e.g. disease or disorder), given exposure to the variable of interest (e.g. health characteristic, aspect of medical history). |
How do you interpret odds ratio and risk ratio? | The odds ratio is interpreted in the same manner as the risk ratio or rate ratio with an OR of 1.0 indicating no association, an OR greater than 1.0 indicating a positive association, and an OR less than 1.0 indicating a negative, or protective association. |
What is the difference between odds ratio and prevalence odds ratio? | Odds ratio (OR) and risk ratio (RR) are two commonly used measures of association reported in research studies. In cross-sectional studies, the odds ratio is also referred to as the prevalence odds ratio (POR) when prevalent cases are included, and, instead of the RR, the prevalence ratio (PR) is calculated. |
- How do you explain prevalence ratio?
- The prevalence ratio (PR) is analogous to the risk ratio (RR) of cohort studies. The denominators for both ratios are fixed populations – fixed at the start of the study in the case of a cohort study, and fixed at the point or period of time for the case-control study.
- How do you interpret the odds ratio proportion?
- Important points about Odds ratio: OR >1 indicates increased occurrence of an event. OR <1 indicates decreased occurrence of an event (protective exposure) Look at CI and P-value for statistical significance of value (Learn more about p values and confidence intervals here) In rare outcomes OR = RR (RR = Relative Risk)
- How do you interpret risk differences?
- The risk difference is straightforward to interpret: it describes the actual difference in the observed risk of events between experimental and control interventions; for an individual it describes the estimated difference in the probability of experiencing the event.