Trang Nguyen - Academia.edu (original) (raw)
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Papers by Trang Nguyen
Psychological Methods
Causal mediation analysis is complicated with multiple effect definitions that require different ... more Causal mediation analysis is complicated with multiple effect definitions that require different sets of assumptions for identification. This paper provides a systematic explanation of such assumptions. We define five potential outcome types whose means are involved in various effect definitions. We tackle their mean/distribution's identification, starting with the one that requires the weakest assumptions and gradually building up to the one that requires the strongest assumptions. This presentation shows clearly why an assumption is required for one estimand and not another, and provides a succinct table from which an applied researcher could pick out the assumptions required for identifying the causal effects they target. Using a running example, the paper illustrates the assembling and consideration of identifying assumptions for a range of causal contrasts. For several that are commonly encountered in the literature, this exercise clarifies that identification requires weaker assumptions than those often stated in the literature. This attention to the details also draws attention to the differences in the positivity assumption for different estimands, with practical implications. Clarity on the identifying assumptions of these various estimands will help researchers conduct appropriate mediation analyses and interpret the results with appropriate caution given the plausibility of the assumptions.
Microbiology, 2009
Streptococcus mutans is considered a primary pathogen for human dental caries. Its ability to pro... more Streptococcus mutans is considered a primary pathogen for human dental caries. Its ability to produce a variety of peptide antibiotics called mutacins may play an important role in its invasion and establishment in the dental biofilm. S. mutans strain UA140 produces two types of mutacins, the lantibiotic mutacin I and the non-lantibiotic mutacin IV. In a previous study, we constructed a random insertional-mutation library to screen for genes involved in regulating mutacin I production, and found 25 genes/operons that have a positive effect on mutacin I production. In this study, we continued our previous work to identify genes that are negatively involved in mutacin I production. By using a high-phosphate brain heart infusion agar medium that inhibited mutacin I production of the wild-type, we isolated 77 clones that consistently produced mutacin I under repressive conditions. From the 34 clones for which we were able to obtain a sequence, 17 unique genes were identified. These gene...
This paper studies the recent boom and bust in Vietnam's coffee economy. Data from smallholder co... more This paper studies the recent boom and bust in Vietnam's coffee economy. Data from smallholder coffee farms in the Central Highlands are used to examine responses to a drop in producer coffee prices. A multinomial logistic regression model is used to identify several factors associated with four specific patterns observed among coffee farmers: no response to price change, reductions in use of purchased inputs, changes in crop mix, and responses aimed at enhancing liquidity through off-farm work or borrowing. Patterns of response are shown to have differed systematically across subgroups of smallholders. Policy implications raised by the findings are discussed.
Psychological Methods
Causal mediation analysis is complicated with multiple effect definitions that require different ... more Causal mediation analysis is complicated with multiple effect definitions that require different sets of assumptions for identification. This paper provides a systematic explanation of such assumptions. We define five potential outcome types whose means are involved in various effect definitions. We tackle their mean/distribution's identification, starting with the one that requires the weakest assumptions and gradually building up to the one that requires the strongest assumptions. This presentation shows clearly why an assumption is required for one estimand and not another, and provides a succinct table from which an applied researcher could pick out the assumptions required for identifying the causal effects they target. Using a running example, the paper illustrates the assembling and consideration of identifying assumptions for a range of causal contrasts. For several that are commonly encountered in the literature, this exercise clarifies that identification requires weaker assumptions than those often stated in the literature. This attention to the details also draws attention to the differences in the positivity assumption for different estimands, with practical implications. Clarity on the identifying assumptions of these various estimands will help researchers conduct appropriate mediation analyses and interpret the results with appropriate caution given the plausibility of the assumptions.
Microbiology, 2009
Streptococcus mutans is considered a primary pathogen for human dental caries. Its ability to pro... more Streptococcus mutans is considered a primary pathogen for human dental caries. Its ability to produce a variety of peptide antibiotics called mutacins may play an important role in its invasion and establishment in the dental biofilm. S. mutans strain UA140 produces two types of mutacins, the lantibiotic mutacin I and the non-lantibiotic mutacin IV. In a previous study, we constructed a random insertional-mutation library to screen for genes involved in regulating mutacin I production, and found 25 genes/operons that have a positive effect on mutacin I production. In this study, we continued our previous work to identify genes that are negatively involved in mutacin I production. By using a high-phosphate brain heart infusion agar medium that inhibited mutacin I production of the wild-type, we isolated 77 clones that consistently produced mutacin I under repressive conditions. From the 34 clones for which we were able to obtain a sequence, 17 unique genes were identified. These gene...
This paper studies the recent boom and bust in Vietnam's coffee economy. Data from smallholder co... more This paper studies the recent boom and bust in Vietnam's coffee economy. Data from smallholder coffee farms in the Central Highlands are used to examine responses to a drop in producer coffee prices. A multinomial logistic regression model is used to identify several factors associated with four specific patterns observed among coffee farmers: no response to price change, reductions in use of purchased inputs, changes in crop mix, and responses aimed at enhancing liquidity through off-farm work or borrowing. Patterns of response are shown to have differed systematically across subgroups of smallholders. Policy implications raised by the findings are discussed.