Simple linear regression is a model that assesses the relationship between a dependent variable and an independent variable. 

The simple linear model is expressed using the following equation: 

Y = β0+ β1X i+ εi

Xi Is independent Yi is dependent.

Example : Between income and happiness. Survey OF 600 people whose incomes range from $25k to $85k and ask them to rank their happiness on a scale from 1 to 10.

Here the independent variable (income) and dependent variable (happiness) are both quantitative.