library(foreign) library(dplyr) data_URL <- "https://github.com/mca91/EconometricsWithR/blob/master/data/fastfood.dta?raw=true" dat <- read.dta(data_URL) dat <- dat %>% mutate(FTE = nmgrs + empft + (0.5 * emppt), FTE2 = nmgrs2 + empft2 + (0.5 * emppt2)) dat_NJ <- subset(dat, state == 1) dat_PA <- subset(dat, state == 0) # test if the difference in mean employment in New Jersey is zero before and after the wage increase # test if the difference in mean employment in New Jersey is zero before and after the wage increase t.test(dat_NJ$FTE, dat_NJ$FTE2) ex() %>% check_predefined_objects(c("dat", "dat_NJ", "dat_PA")) ex() %>% check_or( ex() %>% check_function("t.test") %>% check_result() %>% check_equal(), override_solution(., "t.test(dat_NJ$FTE2, dat_NJ$FTE)") %>% check_function("t.test") %>% check_result() %>% check_equal(incorrect_msg = "Your call of `t.test()` is not correct.")) success_msg(msg = "Corect! Since the p-value is 0.4191 we cannot reject the null hypothesis that there is no differnce in average employment in New Jersey before and after the minimum wage increase.")