# Stata: Bivariate Regression

In this post we’ll use the system dataset auto.

```sysuse auto, clear
```

To estimate the model we use the `regress` command in the command window. The `regress` command follows the general format of `regress dv iv, options`. Type `help regress` or visit the online help for `regress` for a description of the options available for regress. For example the regression of price on mpg is estimated as follows:

```regress price mpg
```

The output includes:

1. The ANOVA source table
2. Descriptive statistics and effect sizes
3. Coefficients, hypothesis tests, and confidence intervals

## Standardized Coefficients

Suppose we would like Stata to report standardized coefficients. To get standardized coefficients we add the `beta` option to our command.

```regress price mpg, beta
```

## Visualizing Regression Lines

We can visualize the relationship between two variables with a scatterplot. Stata’s graphics provide several useful commands for including regression lines on a scatterplot. We’ll discuss the `lfit` and `lfitci` commands.

To produce a scatterplot between price (y-axis) and mpg (x-axis), we use the `graph twoway scatter` command.

```graph twoway scatter price mpg
```

Now let’s add the regression line to the plot. The `lfit` graph command allows us to do this (`lfit` stands for linear fit). However, we don’t want the regression line in isolation. We want it on top of the scatterplot. Stata lets you combine twoway graphs in one of two ways: (1) using parentheses or (2) using pipes. To add the regression line with parentheses, we type:

```graph twoway (lfit price mpg) (scatter price mpg)
```

The first set of parentheses is the regression line and the second is the scatterplot. This produces the following plot:

To add the regression line with pipes (this produces an identical plot as above), we type:

```graph twoway lfit price mpg || scatter price mpg
```

It can be nice to include confidence intervals on the plot. To do this we simply change the `lfit` command to `lfitci`, where the `ci` refers to confidence interval.

```graph twoway lfitci price mpg || scatter price mpg
```