year - observation year
state - state (FIPS code)
legal1820 - percentage of 18-20 year olds who can legally drink
dtype - death cause (4 types)
pop - state population
mrate - mortality rate per 100,000/year

mortality rate = α+ δDDLEGALst + βSTATEs + γYEARt + εst
DDLEGALst - proportion of 18-20 year olds that can drink in state s at time t
STATEs is the dummy variable for each state
YEARt is the dummy variable for each year
εst - error term

deathall <- subset(mlda_data, mlda_data$dtype == 1)
deathmotor <- subset(mlda_data, mlda_data$dtype == 2)
deathsuicide <- subset(mlda_data, mlda_data$dtype == 3)
deathinternal <- subset(mlda_data, mlda_data$dtype == 6)

deathall$statedummy = ifelse(deathall$legal1820 < 100, 1, 0)
deathall$yeardummy = ifelse(deathall$legal1820 < 100, 1, 0)

deathall$did = deathall$statedummy * deathall$yeardummy
deathall_baseline = lm(mrate ~ statedummy + yeardummy + did, data = deathall)

> summary(deathall_baseline)

Call:
lm(formula = mrate ~ statedummy + yeardummy + did, data = deathall)

Residuals:
Min      1Q  Median      3Q     Max
-88.214 -24.803  -6.004  14.797 191.199

Coefficients: (2 not defined because of singularities)
        Estimate Std. Error t value Pr(>|t|)
(Intercept)  130.014      2.302  56.478  < 2e-16 ***
statedummy    10.674      2.966   3.598 0.000343 ***
yeardummy         NA         NA      NA       NA
did               NA         NA      NA       NA
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 38.79 on 712 degrees of freedom
Multiple R-squared:  0.01786,   Adjusted R-squared:  0.01648
F-statistic: 12.95 on 1 and 712 DF,  p-value: 0.0003425

deathall_statepop = lm(mrate ~ statedummy + yeardummy + pop + state + did, data = deathall)