## ----setup, include = FALSE---------------------------------------------------
knitr::opts_chunk$set(
  collapse = TRUE,
  comment  = "#>",
  fig.width  = 6,
  fig.height = 4
)
library(pft)
set.seed(7)

## -----------------------------------------------------------------------------
# Box 2 worked example: 14-year-old male, FEV1 z dropped from -0.78
# to -1.60 over 3 months.
pft_change(z1 = -0.78, z2 = -1.60, age_t1 = 14, time_years = 0.25)

## -----------------------------------------------------------------------------
pft_change(z1 = -0.78, z2 = -1.60, age_t1 = 14, time_years = 4)

## -----------------------------------------------------------------------------
# Box 3 worked example: 70-year-old female with FEV1 = 0.9 L.
pft_fev1q(fev1 = 0.9, sex = "F", age = 70)

## ----eval = requireNamespace("ggplot2", quietly = TRUE)-----------------------
library(ggplot2)
serial <- data.frame(
  patient_id  = rep(1:2, each = 4),
  visit_date  = rep(as.Date(c("2020-01-15","2021-03-10",
                               "2022-05-20","2023-07-30")), 2),
  fev1_zscore_2022 = c(-0.5, -0.8, -1.2, -1.6,
                   0.2,  0.0, -0.3, -0.5)
)
ggplot(serial, aes(visit_date, fev1_zscore_2022,
                   colour = factor(patient_id), group = patient_id)) +
  geom_hline(yintercept = -1.645, linetype = "dotted") +
  geom_line() + geom_point() +
  labs(x = "Visit date", y = "FEV1 z-score", colour = "Patient") +
  theme_minimal()