Handling missing covariates in observational studies: An illustration with the assessment of prognostic factors of survival outcomes in sarcoma in irradiated fields (SIF).
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request. ### Instruction: Identify all the mentioned drugs in the given text. Text may or may not contain drug. If they contain more than 1 drug, use ";" as delimiter and join them. ### Input: Handling missing covariates in observational studies: An illustration with the assessment of prognostic factors of survival outcomes in sarcoma in irradiated fields (SIF). ### Output: 