Significance Test of Proportions: Perpetrators of Mass Shootings in the U.S. between 2013 and 2025

# Load required packages
library(ggplot2)
library(dplyr)

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

library(tibble)
library(ggthemes)

# ----------------------------
# 1. Define totals
# ----------------------------

total_events <- 5748

# ----------------------------
# 2. Create dataset (3 groups)
# ----------------------------

data <- tibble(
  Group = c("Transgender", "Cis-Gendered White Men", "Other"),
  Observed = c(5, 5690, 53),
  Population_Percent = c(0.016, 0.47, 0.514)
)

# ----------------------------
# 3. Expected counts
# ----------------------------

data <- data %>%
  mutate(
    Expected = total_events * Population_Percent
  )

# ----------------------------
# 4. Chi-square goodness-of-fit test
# ----------------------------

chisq_test <- chisq.test(
  x = data$Observed,
  p = data$Population_Percent
)

chisq_test

    Chi-squared test for given probabilities

data:  data$Observed
X-squared = 6237.4, df = 2, p-value < 2.2e-16

# ----------------------------
# 5. Per-capita rate
# ----------------------------

data <- data %>%
  mutate(
    Rate_per_1pct = Observed / (Population_Percent * 100)
  )

data

# A tibble: 3 × 5
  Group                  Observed Population_Percent Expected Rate_per_1pct
  <chr>                     <dbl>              <dbl>    <dbl>         <dbl>
1 Transgender                   5              0.016     92.0          3.12
2 Cis-Gendered White Men     5690              0.47    2702.         121.  
3 Other                        53              0.514   2954.           1.03

# ----------------------------
# 6. Plot
# ----------------------------

ggplot(data, aes(x = Group, y = Rate_per_1pct)) +
  geom_col() +
  labs(
    title = "Per Capita Event Rate by Group",
    y = "Events per 1% of Population",
    x = ""
  ) +
  theme_economist()

Sources:

Gun Violence Archive

Pew Research Center