To use this function, choose .
Calculates row-by-row differences between numeric values in a column. You specify the lag (number of rows); Minitab subtracts the value in current row from the value in the lag row.
In number, specify the column. Minitab subtracts from each row the element lag rows above, and stores the differences in a new column. If you don't specify a value for lag, the differences are calculated between consecutive rows (lag = 1). The first lag rows of the new column will contain the missing value symbol *.
A store manager records the number of customer complaints each month. To monitor monthly variation the manager wants to determine the row-by-row differences in the number of complaints. In , the manager enters the expression DIFFERENCES(C1,1) and stores the results in C2.
Calculating differences can also be an important step in finding trends or seasonality that may affect the data. For example, a toy store company wants to use a times series (ARIMA model) to predict monthly sales. However, they suspect a strong seasonal impact on monthly sales; toy sales in December are always higher than other months due to the holiday season.
To make the data more stationary and help reveal any underlying seasonal pattern before choosing a model, they first calculate differences in monthly sales using a lag of 12. Then they assess autocorrelation of the differences using .