---
title: "Session 11 — Confidence interval"
author: "Prof. Dae-Jin Lee (daelee@faculty.ie.edu)"
date: "Fall 2026"
output:
  html_document:
    theme: flatly
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE, message = FALSE, warning = FALSE)
library(tidyverse)
```

```{r}
survey <- read_csv("data/survey_attitudes.csv")
set.seed(11)
samp <- survey |> slice_sample(n = 40)

t.test(samp$support_international_cooperation)
t.test(samp$support_international_cooperation)$conf.int
```

**Interpret carefully:** this interval comes from a procedure with ~95% coverage under random sampling assumptions. It is **not** “95% of respondents score inside the interval.”