The main types of data patterns are level or horizontal, trend, seasonality and cycles. Level patterns show a stable demand that fluctuates some around the mean. The demand for some food items is relatively stable. A trend is where the data is either increasing or decreasing rather steadily over time. For example, the current trend in computer sales has been decreasing in the U.S. because less people need to upgrade their computers. Seasonality occurs when the season affects the level of demand. For example, computer sales increase during the Christmas season dramatically. Cycles are movements in the data up and down over longer periods of time. The demand for housing tends to follow a cyclical pattern based on the interest rates and other economic factors.