作为R和gtsummary的初学者，我在制作tbl_summary时遇到了一个问题。FEV 1前、FVC前、FEV 1后和FVC后的数据不符合我的预期。前FEV 1和前FVC以及后FEV 1和后FVC的缺失值相同，因此我希望每对仅缺失1行。更棒的是将2对“分组”如下：
| 支气管扩张剂前肺量测定|
| FEV1| {mean}（{sd}）|......这是什么？
| FVC| {mean}（{sd}）|......这是什么？
| 支气管扩张剂后肺量测定|
| FEV1| {mean}（{sd}）|......这是什么？
| FVC| {mean}（{sd}）|......这是什么？
这是我目前的代码为下表

Tib1 <- Data %>%
+   select(c(sex, alder_basis, etnisknavn, udd1, udd2, lsprefev, lsprefvc, lspostfev, lspostfvc, av)) %>%
+   unlabelled() %>%
+   tibble()
> Tib1$lspostfvc <- as.double(Tib1$lspostfvc)
> Tib1$av <- fct_na_value_to_level(Tib1$av,level = "NA")
> Tib1
> Tbl1 <- tbl_summary(Tib1, 
+             by = av,
+             value = list(sex ~ "Female", etnisknavn ~ "No Danish descent"),
+             label = list(sex ~ "Female", etnisknavn ~ "Non-Danish descent", alder_basis ~ "Age (as of January 1st 2004)", lspostfvc ~ "Post FVC"),
+             statistic = list(
+               all_continuous() ~ "{mean} ({sd})",
+               all_categorical() ~ "{n} ({p}%)"),
+             digits = c(alder_basis) ~ 1, 
+             missing_text = "(Missing, n)"
+             ) %>%
+   add_p() %>%
+   add_overall() %>%
+   modify_spanning_header(c("stat_1":"stat_8") ~ "**Age of AC debut**") %>%
+   modify_caption("**Table 1. Patient Characteristics**") %>%
+   modify_footnote(
+     update = all_stat_cols() ~ 
+       "mean (SD) for continous; n (%) for categorical"
+   )
> 
> Tbl1

My current summary table showing pre-FEV1, pre-FVC, post-FEV1 and post-FVC as individual variables and each with corresponding missing values