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Table 2 Summary of methods, research questions best answered, and findings

From: An overview of methods to address distinct research questions on environmental mixtures: an application to persistent organic pollutants and leukocyte telomere length

MethodResearch QuestionResults
Unsupervised Methods
K-means Clustering Hierarchical ClusteringAre there population subgroups that share similar exposure profiles?The study population is clustered by level of exposure: high, average, and low. High exposure is associated with longer log-LTL.
PCAAre there specific patterns in POP exposure?Three patterns of exposure were identified. Exposure to all POPs (PC1) is associated with longer log-LTL.
EFA Four patterns of exposure were identified. Exposure to all four furans (FA2) and to PCBs 118 and 126 (FA3) is associated with longer log-LTL.
Supervised Methods
LassoWhich congeners are associated with changes in log-LTL?PCB 99, PCB 118, PCB 126, and furan 2,3,4,7,8-pncdf are associated with longer log-LTL.
Elastic Net PCB 99, PCB 118, PCB 126, furan 2,3,4,7,8-pncdf, and furan 1,2,3,4,6,7,8 hxcdf are associated with longer log-LTL.
Group LassoWhich a priori defined congener groups are associated with changes in log-LTL and what is the magnitude of the association with congeners within those groups?All mPFD congeners are associated with log-LTL, with variability in direction—five mPFDs with longer log-LTL, and three mPFDs with shorter log-LTL. Non-ortho PCBs (PCBs 126 and 169) are associated with longer log-LTL.
WQSWhat is the overall effect of the mixture on log-LTL? What congeners are most important?The mixture index is associated with longer log-LTL. Three furans and both non-ortho PCBs are important mixture members. Furans 1,2,3,4,6,7,8-hxcdf and 2,3,4, 7,8-pncdf has the largest weights.
BKMRIs there an association between the mixture and log-LTL? What is the exposure-response relationship between each congener and log-LTL? Are there interactions between congeners?The overall mixture is associated with longer log-LTL. Furan 2,3,4,7,8-pncdf, PCB 126, and PCB 169 are independently associated with longer log-LTL. No interactions or nonlinearities were found.
  1. All 18 congeners were included in all unsupervised and supervised models