# Alcohol Counts

Counts involving alcohol are complicated due to a high rate of missing BAC values. FARS and GESCRSS include the variables `alc_res` (BAC values) and `dr_drink` (police-reported alcohol involvement). NHTSA also uses multiple imputation (MI) to estimate missing BAC values in FARS records (not GES/CRSS records). Traffic Safety Facts uses MI to report the number of fatalities from crashes involving a driver with a BAC of .08 g/dL or higher. Using `alc_res` and `dr_drink` produce smaller counts than those produced via MI.

`rfars::counts()` counts alcohol-involved crashes, fatalities and injuries using `alc_res` and `dr_drink`. However, the `flat` object returned by `get_fars()` includes the MI variables `a1`:`a10` from the Midrvacc file, and `p1`:`p10` from the Miper file. Below we explore the differences and show how to use the MI variables to replicate NHTSA’s reporting. See Appendix E of the FARS Analytical User’s Manual for more information on these files.

    library(dplyr)
    library(ggplot2)

    ## Warning: package 'ggplot2' was built under R version 4.4.3

    library(tidyr)
    library(rfars)

Here we use `rfars::counts()` to count alcohol-involved crashes in 2023:

    myFARS <- get_fars(years = 2023, proceed = TRUE)
    counts(myFARS, involved = 'alcohol') %>% knitr::kable(format = "html")

year | what | states | region | urb | who | involved | n
--- | --- | --- | --- | --- | --- | --- | ---
2020 | crashes | all | all | all | all | alcohol | 259
2021 | crashes | all | all | all | all | alcohol | 267
2022 | crashes | all | all | all | all | alcohol | 259
2023 | crashes | all | all | all | all | alcohol | 235
2024 | crashes | all | all | all | all | alcohol | 8990

    ## Note: rfars::counts() uses the variables alc_res and dr_drink to determine alcohol involvement. NHTSA reports counts using multiple imputation to estimate missing BAC values. See vignette('Alcohol Counts', package = 'rfars') for more information.

And here we use `rfars::counts()` to count the number of alcohol-involved fatalities in the same year:

    counts(
      df = myFARS,
      what = "fatalities",
      involved = 'alcohol'
    ) %>%
      knitr::kable(format = "html")

year | what | states | region | urb | who | involved | n
--- | --- | --- | --- | --- | --- | --- | ---
2020 | fatalities | all | all | all | all | alcohol | 282
2021 | fatalities | all | all | all | all | alcohol | 282
2022 | fatalities | all | all | all | all | alcohol | 274
2023 | fatalities | all | all | all | all | alcohol | 254
2024 | fatalities | all | all | all | all | alcohol | 9979

    ## Note: rfars::counts() uses the variables alc_res and dr_drink to determine alcohol involvement. NHTSA reports counts using multiple imputation to estimate missing BAC values. See vignette('Alcohol Counts', package = 'rfars') for more information.

The MI process produces 10 separate BAC estimates. The Miper file provides `p1`:`p10`, person level BAC estimates for each driver and non-occupant in the FARS Person data file. The Midrvacc file provides variables `a1`:`a10`, crash level BAC estimates derived from driver records in the Miper file.

To replicate the estimated number of fatalities reported in Traffic Safety Facts, we implement the procedure below.

Step 1. Start with the `flat` object and filter to fatalities. Then generate 30 indicator variables, 10 `FPC_i`, 10 `SPC_i`, and 10 `TPC_i` variables. `i` corresponds to the 10 `a_i` and `p_i` variables. FPC indicates that BAC = 0.00, SPC that BAC is between 0.01 and 0.07, and TPC that BAC is >= 0.08. So if `a_1` = 5 (representing a BAC of 0.05), then `FPC_1` = 0, `SPC_1` = 1, and `TPC_1` = 0.

    temp <- myFARS$flat %>%
      select(year:per_no, age, sex, per_typ, inj_sev, alc_res, dr_drink, a1:a10) %>%
      filter(inj_sev == "Fatal Injury (K)")

    for(i in 1:10) {
      imputation_col <- paste0("a", i)
      temp[[paste0("FPC", i)]] <- ifelse(temp[[imputation_col]] == 0, 1, 0)  # BAC = 0.00
      temp[[paste0("SPC", i)]] <- ifelse(temp[[imputation_col]] >= 1 & temp[[imputation_col]] <= 7, 1, 0)  # BAC = 0.01-0.07
      temp[[paste0("TPC", i)]] <- ifelse(temp[[imputation_col]] >= 8, 1, 0)  # BAC = 0.08+
    }

This produces the table below (transposed for easier viewing).

    temp %>%
      select(st_case, a1:a10, starts_with("FPC"), starts_with("SPC"), starts_with("TPC")) %>%
      slice(1:10) %>%
      t() %>%
      knitr::kable(format = "html")

st_case | 510001 | 510002 | 510003 | 510004 | 510005 | 510006 | 510007 | 510008 | 510009 | 510011
a1 | 0 | 0 | 23 | 28 | 21 | 0 | 0 | 6 | 23 | 0
a2 | 0 | 0 | 0 | 28 | 21 | 0 | 0 | 6 | 23 | 0
a3 | 0 | 0 | 5 | 28 | 21 | 0 | 0 | 6 | 23 | 0
a4 | 0 | 0 | 0 | 28 | 21 | 0 | 0 | 6 | 23 | 0
a5 | 0 | 0 | 13 | 28 | 21 | 0 | 0 | 6 | 23 | 0
a6 | 0 | 0 | 21 | 28 | 21 | 0 | 0 | 6 | 23 | 0
a7 | 21 | 0 | 28 | 28 | 21 | 0 | 0 | 6 | 23 | 0
a8 | 0 | 0 | 0 | 28 | 21 | 0 | 0 | 6 | 23 | 0
a9 | 0 | 5 | 23 | 28 | 21 | 0 | 0 | 6 | 23 | 0
a10 | 0 | 0 | 0 | 28 | 21 | 0 | 0 | 6 | 23 | 0
FPC1 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1
FPC2 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1
FPC3 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1
FPC4 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1
FPC5 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1
FPC6 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1
FPC7 | 0 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1
FPC8 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1
FPC9 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1
FPC10 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1
SPC1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0
SPC2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0
SPC3 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0
SPC4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0
SPC5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0
SPC6 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0
SPC7 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0
SPC8 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0
SPC9 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0
SPC10 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0
TPC1 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 0
TPC2 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0
TPC3 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0
TPC4 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0
TPC5 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 0
TPC6 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 0
TPC7 | 1 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 0
TPC8 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0
TPC9 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 0
TPC10 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0

We can examine one crash to see the relation between the `a` and `FPC`, `SPS`, and `TPC` variables. The table below shows the 10 iterations for `a`, and the corresponding indicator variables.

    temp %>%
      slice(1) %>%
      select(st_case, a1:a10, starts_with("FPC"), starts_with("SPC"), starts_with("TPC")) %>%
      pivot_longer(-1) %>%
      mutate(
        iter = gsub("\\D", "", name),
        name = gsub("[^A-Za-z]", "", name)
      ) %>%
      pivot_wider() %>%
      knitr::kable(format = "html")

st_case | iter | a | FPC | SPC | TPC
--- | --- | --- | --- | --- | ---
510001 | 1 | 0 | 1 | 0 | 0
510001 | 2 | 0 | 1 | 0 | 0
510001 | 3 | 0 | 1 | 0 | 0
510001 | 4 | 0 | 1 | 0 | 0
510001 | 5 | 0 | 1 | 0 | 0
510001 | 6 | 0 | 1 | 0 | 0
510001 | 7 | 21 | 0 | 0 | 1
510001 | 8 | 0 | 1 | 0 | 0
510001 | 9 | 0 | 1 | 0 | 0
510001 | 10 | 0 | 1 | 0 | 0

Step 2. Sum the indicator variables in each iteration.

    case_results <- list()

    for(i in 1:10) {
      fpc_col <- paste0("FPC", i)
      spc_col <- paste0("SPC", i)
      tpc_col <- paste0("TPC", i)

      case_results[[i]] <-
        temp %>%
        summarise(
          TOTAL = n(),
          !!paste0("FSBAC", i) := sum(!!sym(fpc_col), na.rm = TRUE),
          !!paste0("SSBAC", i) := sum(!!sym(spc_col), na.rm = TRUE),
          !!paste0("TSBAC", i) := sum(!!sym(tpc_col), na.rm = TRUE),
          .groups = 'drop'
        )
    }

This produces 10 estimates of the number of fatalities from crashes where BAC = 0 (FSBAC), where BAC was between 0.01 and 0.07 (SSBAC), and where BAC >= 0.08 (TSBAC). The table below shows all of these estimates.

    bind_rows(
      data.frame(case_results[[1]])  %>% select(TOTAL, FSBAC=2, SSBAC=3, TSBAC=4) %>% mutate(iter=1),
      data.frame(case_results[[2]])  %>% select(TOTAL, FSBAC=2, SSBAC=3, TSBAC=4) %>% mutate(iter=2),
      data.frame(case_results[[3]])  %>% select(TOTAL, FSBAC=2, SSBAC=3, TSBAC=4) %>% mutate(iter=3),
      data.frame(case_results[[4]])  %>% select(TOTAL, FSBAC=2, SSBAC=3, TSBAC=4) %>% mutate(iter=4),
      data.frame(case_results[[5]])  %>% select(TOTAL, FSBAC=2, SSBAC=3, TSBAC=4) %>% mutate(iter=5),
      data.frame(case_results[[6]])  %>% select(TOTAL, FSBAC=2, SSBAC=3, TSBAC=4) %>% mutate(iter=6),
      data.frame(case_results[[7]])  %>% select(TOTAL, FSBAC=2, SSBAC=3, TSBAC=4) %>% mutate(iter=7),
      data.frame(case_results[[8]])  %>% select(TOTAL, FSBAC=2, SSBAC=3, TSBAC=4) %>% mutate(iter=8),
      data.frame(case_results[[9]])  %>% select(TOTAL, FSBAC=2, SSBAC=3, TSBAC=4) %>% mutate(iter=9),
      data.frame(case_results[[10]]) %>% select(TOTAL, FSBAC=2, SSBAC=3, TSBAC=4) %>% mutate(iter=10)
      ) %>%
      knitr::kable(format = "html")

TOTAL | FSBAC | SSBAC | TSBAC | iter
--- | --- | --- | --- | ---
42997 | 27704 | 2180 | 13030 | 1
42997 | 27698 | 2208 | 13008 | 2
42997 | 27624 | 2246 | 13044 | 3
42997 | 27784 | 2218 | 12912 | 4
42997 | 27326 | 2237 | 13351 | 5
42997 | 27637 | 2240 | 13037 | 6
42997 | 27758 | 2159 | 12997 | 7
42997 | 27669 | 2198 | 13047 | 8
42997 | 27820 | 2273 | 12821 | 9
42997 | 27721 | 2213 | 12980 | 10

Step 3. Take the average of each set of estimates.

    calc <- case_results[[1]]

    for(i in 2:10) {
      calc <- calc %>% bind_cols(case_results[[i]] %>% select(-TOTAL))
    }

    calc <-
      calc %>%
      rowwise() %>%
      mutate(
        SBAC0 = round(mean(c_across(starts_with("FSBAC")), na.rm = TRUE)), # BAC 0.00
        SBAC1 = round(mean(c_across(starts_with("SSBAC")), na.rm = TRUE)), # BAC 0.01-0.07
        SBAC2 = round(mean(c_across(starts_with("TSBAC")), na.rm = TRUE))  # BAC 0.08+
      ) %>%
      ungroup()

This gives us our answer. The values below give the final estimates of the number of fatalities from crashes where BAC = 0 (SBAC0), where BAC was between 0.01 and 0.07 (SBAC1), and where BAC >= 0.08 (SBAC2). The value for SBAC2 is 12,429, which matches Traffic Safety Facts for 2023.

    select(calc, SBAC0:SBAC2) %>% knitr::kable(format = "html")

SBAC0 | SBAC1 | SBAC2
--- | --- | ---
27674 | 2217 | 13023

Shortcut. We can do this more directly if we’re only interested in the number of fatalities from crashes with alcohol-impaired drivers:

    x <-
      myFARS$flat %>%
      select(year:per_no, age, sex, per_typ, inj_sev, alc_res, dr_drink, a1:a10) %>%
      filter(inj_sev == "Fatal Injury (K)") %>%
      mutate_at(paste0("a", 1:10), function(x) 1*(x>=8)) %>%
      group_by(year) %>%
      summarize_at(paste0("a", 1:10), sum, na.rm=T) %>%
      rowwise() %>%
      mutate(a = round(mean(c_across(a1:a10))))

    x$a

    ## [1]   282   284   289   264 11904

Please see Transitioning to Multiple Imputation – A New Method to Impute Missing BAC values in FARS for more guidance on generating other counts using the MI data.