According to Chase, Jacobs, and Aquilano (2006), there are four forecasting techniques: qualitative, time series analysis, casual relationships, and simulation. Qualitative techniques are subjective and judgmental. Time series analysis uses past data to predict the future demand. Casual relationships are when one occurrence causes another to happen. Finally, there are simulation models. These models involve assumptions in regards to internal variables and the external environment. It was stated previously in a separate document that GWI did not use a specific forecasting method, after further research into how GWI predicts the workload for the year, that information is incorrect. GWI uses time series analysis in the prediction of the expected yearly workload. GWI takes the forecast volumes from their top 10 customers and uses that information in conjunction with the data collected from the previous two years to estimate the workload for the upcoming year. Once the yearly forecast is predicted, GWI management also monitors the volumes on a monthly basis by using monthly data from the previous year and 30 and 60 day forecasts from their top 10 customers.