The case-crossover study design for evaluating short-, intermediate-, and long-term exposure effects "1_TS_short.R": R scripts for time-stratified case-crossover design for short-term exposure "2.1_TS_intermediate.R": R scripts for time-stratified case-crossover design for intermediate-term exposure "2.2_SB_intermediate.R": R scripts for symmetric bidirectional case-crossover design for intermediate-term exposure "3_SB_long.R": R scripts for symmetric bidirectional case-crossover design for long-term exposure