cpi_broad_based.R

library(tidyverse)
library(readabs)

# This data contains groups, sub-groups, and expenditure classes
cpi_t13 <- read_abs("6401.0", "13")

# Fetch a list of expenditure classes, as we want to filter to just those
cpi_t14 <- read_abs("6401.0", 14)

exp_classes <- cpi_t14 |>
  pull(series) |>
  unique() |>
  str_remove("Combined Seasonal Adjustment Factors ;") |>
  paste(collapse = "|")

# 3% threshold, in quarterly annualised terms
threshold <- 1.03^(1/4)-1

above_target <- cpi_t13 |>
  filter(str_detect(series, exp_classes),
         !is.na (value)) |>
  group_by(series) |> 
  mutate(quarterly_growth = (value / lag(value, 1, order_by = date)) - 1) |> 
  filter(!is.na(value)) |> 
  group_by(date) |>
  summarise(num_above_target = sum(quarterly_growth > threshold, na.rm = TRUE),
            n = n())  |>
  mutate(prop_above_target = num_above_target / n) 

# Make the chart!
above_target |>
  filter(year(date) >= 1998) |> 
  ggplot(aes(x = date, y = prop_above_target)) +
  geom_line() +
  theme_minimal() +
  scale_y_continuous (labels = scales:: percent,
                      limits = c(.1, 1),
                      expand = expansion(0)) +
  theme(axis.title = element_blank() ) +
  labs(subtitle= "Proportion of CPI expenditure classes with ›3% annual inflation",
       caption = "Source: ABS CPI")