``````library(tidyverse)
library(patchwork)``````

### Inferential statistics

• Inferential statistical analysis infers properties of a population, for example by testing hypotheses and deriving estimates.
• It is assumed that the observed data set is sampled from a larger population.

# 1. Estination and statistical hypothesis testing

• Inferential statistics consist of `estimation` and `statistical hypothesis testing`.
• `Estimation` is the process of finding an estimate, or approximation, which is a value that is usable for some purpose even if input data may be incomplete.
• A `statistical hypothesis test` is a method of statistical inference.
• A statistical hypothesis is a hypothesis that is testable on the basis of observed data modelled as the realised values taken by a collection of random variables.

# 2. Statistical population and Sample

## 2.1 `The number of samples` & `Sample size`

• In statistics, a `population` is a set of similar items or events which is of interest for some question or experiment.

• In social science, a `population` is usually what we are interested in and what we want to know about, such as the average height of Japanese, or the average income of Americans which is not usually accessible due to huge amount of costs.

• In statistics, a `sample` is a set of individuals or objects collected or selected from a statistical population by a defined procedure.