A comparison of approaches for estimating combined population attributable risks (PARs) for multiple risk factors
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Yibing Ruan
, Stephen D. Walter , Christine M. Friedenreich , Darren R. Brennerund on behalf of the ComPARe Study Team
Abstract
Objectives
The methods to estimate the population attributable risk (PAR) of a single risk factor or the combined PAR of multiple risk factors have been extensively studied and well developed. Ideally, the estimation of combined PAR of multiple risk factors should be based on large cohort studies, which account for both the joint distributions of risk exposures and for their interactions. However, because such individual-level data are often lacking, many studies estimate the combined PAR using a comparative risk assessment framework. It involves estimating PAR of each risk factor based on its prevalence and relative risk, and then combining the individual PARs using an approach that relies on two key assumptions: that the distributions of exposures to the risk factors are independent and that the relative risks are multiplicative. While such assumptions rarely hold true in practice, no studies have investigated the magnitude of bias incurred if the assumptions are violated.
Methods
Using simulation-based models, we compared the combined PARs obtained with this approach to the more accurate estimates of PARs that are available when the joint distributions of exposures and risks can be established.
Results
We show that the assumptions of exposure independence and risk multiplicativity are sufficient but not necessary for the combined PAR to be unbiased. In the simplest situation of two risk factors, the bias of this approach is a function of the strength of association and the magnitude of risk interaction, for any values of exposure prevalence and their associated risks. In some cases, the combined PAR can be strongly under- or over-estimated, even if the two assumptions are only slightly violated.
Conclusions
We encourage researchers to quantify likely biases in their use of the M–S method, and here, we provided level plots and R code to assist.
Funding source: Canadian Cancer Society
Award Identifier / Grant number: 703106
Research funding: This research is supported by the Canadian Cancer Society Partner Prevention Research Grant (grant #703106).
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission. All authors contributed equally to this work.
Competing interests: Authors state no conflict of interest.
Proof 1:
exposure independence and risk multiplicativity are sufficient conditions for Miettinen–Steenland approach to be unbiased.
Assume a disease associated with K risk factors is present in a population of N individuals. The disease incidence among non-exposed (i.e., not exposed to any of the K risk factors) is I0. If all K risk factors are dichotomous, then the N individuals can be placed in 2K mutually exclusive strata formed by cross-classifying the risk factors. For risk factor i (i=1, 2,…, K), the marginal prevalence is pi and the unconfounded relative risk is ri (i.e.,
and
Given the independent exposure assumption, the proportion of population in stratum j is the product of all Pij, and the number of individuals in stratum j is
Based on the multiplicative risk assumption, the disease incidence in stratum j is the product of I0 and the relative risks of exposures present in the stratum:
The true combined PAR is the proportion of the excess number of cases from all strata compared to all cases of disease:
Considering any exposure i (for example, let us consider exposure 1, i.e., i=1), the 2K strata can be split into two 2K−1 strata with respect to the presence of exposure 1. The two 2K−1 strata have identical combinations of all other exposures except exposure 1. In the 2K−1 strata that exposure 1 is present, all strata have a common factor of p1r1. In the 2K−1 strata that exposure 1 is absent, all strata have a common factor of 1 × (1 − p1). Therefore,
Using the same approach, each of K the risk factors can be extracted, which results in
The independent exposure and multiplicative risk assumptions also indicate that there are no confounding or effect measure modifications among the K risk factors, in which case the adjusted RR would be equal to unconfounded RR. Therefore,
and therefore
Proof 2:
f(RRa, RRb, Pa, Pb, Y, Z |ra, rb, pa, pb)=0 is a quadratic equation ofY
Because
For f(RRa, RRb, Pa, Pb, Y, Z|ra, rb, pa, pb)=0, it is equivalent that
Define the following terms:
The Mantel–Haenszel adjusted RR can be rearranged as:
And
Similarly
Therefore, the equation can be rearranged as:
This equation is a quadratic equation of Y in the form of A⋅Y2 + B⋅Y + C=0, in which
Potentially, Y has two solutions
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Supplementary Material
The online version of this article offers supplementary material (https://doi.org/10.1515/em-2019-0021).
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Artikel in diesem Heft
- Editorial
- The mean prevalence
- Research Articles
- Heterogeneous indirect effects for multiple mediators using interventional effect models
- Sleep habits and their association with daytime sleepiness among medical students of Tanta University, Egypt
- Population attributable fractions for continuously distributed exposures
- A real-time search strategy for finding urban disease vector infestations
- Disease mapping models for data with weak spatial dependence or spatial discontinuities
- A comparison of cause-specific and competing risk models to assess risk factors for dementia
- A simple index of prediction accuracy in multiple regression analysis
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- Posterior predictive treatment assignment methods for causal inference in the context of time-varying treatments
- Random effects tumour growth models for identifying image markers of mammography screening sensitivity
- Extrapolating sparse gold standard cause of death designations to characterize broader catchment areas
- Extending balance assessment for the generalized propensity score under multiple imputation
- Regression analysis of unmeasured confounding
- The Use of Logic Regression in Epidemiologic Studies to Investigate Multiple Binary Exposures: An Example of Occupation History and Amyotrophic Lateral Sclerosis
- Meeting the Assumptions of Inverse-Intensity Weighting for Longitudinal Data Subject to Irregular Follow-Up: Suggestions for the Design and Analysis of Clinic-Based Cohort Studies