### Null hyposthesis

### Confidence interval
Interval which is expected to contain the parameter
$$
CI = \bar{x} \pm z \frac{s}{\sqrt{n}}
$$
Where $z\frac{s}{\sqrt{n}}$ is the variation in our estimate.


### T-Test
Used to determine if there is a significant difference between the means of two groups.

We have to assume:
- Data follows a normal distribution
- each observation is independent

$$
t = \frac{\text{mean} - \text{theoretical value}}{s\sqrt{n}}
$$