# Researching autocorrelation – past values' influence over present values

In this section, we will learn how to get data errors or residuals from the linear regression model that we want to use as a time-series model to do forecasts. The regression line indicates the trend of data. The Durbin-Watson test uses the errors to see whether there is periodic behavior in the time frame in order to decide whether there is autocorrelation or not.

First, we are going to use the regression function in Excel with the air passenger sales data, as shown in *Figure 11.5*. We have to enter the parameters in the regression function and specify that we want error results. To do this, go to the **Data** option in the **Data Analysis** upper menu and choose **Regression**.

If you cannot find the **Regression** option in **Data Analysis**, you will have to install the **Analysis** tool pack in Excel. To do this, follow these steps:

- Click the
**File**tab, and then go to the**Options**|**Add-ins**category. - In...