I have a huge dataset of questionnaire data. Looking at a subset of items I can see that for each of the items (let's say var1:var50) there are 25 NAs. Whilst it is likely that these 25 NAs are each coming from the same participants across items, I need to actually verify that this is true.

I managed to do this in quite a tedious way and I am looking for a more elegant solution to the problem.

Here a working example of my solution in R:

```
ID <- 1:10
var1 <- c(1,2,3,2,1,NA,1,3,2,NA)
var2 <- c(2,1,3,1,2,NA,3,2,1,NA)

df <- data.frame(ID,var1,var2)
df[which(is.na(df$var1 & df$var2)),]$ID

```

As you can see I would need to write down all individual variable names which can be very tedious when it comes to 50 or more questionnaire items.