A little expansion as to why deflation is usually regard as worse: is that it becomes exponential, in the sense that consumers understand that prices will fall and therefore continuously put off purchasing. And for the reasons aforementioned it is extremely difficult to get out of. A favourite case study of mine is America during the 1930s. It experienced a fall in the average price level of roughly 50%. Which required pretty much WW2 to end. (This is a short explanation, the effect of the ND & WW2 on America's reflation is an area of controversy, but would be enough if you want to give as an example in economics).