Performs symmetric trimming based on minimum propensity score across all treatment groups. Implements the Crump extension to multiple treatments as described in Yoshida et al. (2019).
trim_weights_symmetric(ps_result, data, treatment_var, delta = NULL)A logical vector of length n, where TRUE indicates the observation should be kept and FALSE indicates it should be trimmed.
A list returned by estimate_ps().
A data.frame containing the treatment variable.
A character string specifying the name of the treatment
variable in data.
Numeric trimming threshold in (0, 1/J] where J is the number of treatment levels. Default is NULL, which uses recommended values: 0.1 for binary treatment, 0.067 for 3 groups, 1/(2*J) for J >= 4.
The symmetric trimming rule retains observation i if: $$\min_j\{e_{ji}\} \geq \delta$$
For binary treatment (J=2), this reduces to: \(e(X) \in [\delta, 1-\delta]\).
Yoshida, K., et al. (2019). Multinomial extension of propensity score trimming methods: A simulation study. American Journal of Epidemiology, 188(3), 609-616.