History of the United States (1918–1945) (especially poor people) and prevent inflation. Tires were the first item to be rationed in January 1942 because supplies of natural rubber were interrupted. Gasoline rationing proved an even better way to allocate scarce rubber. By 1943 one needed government issued ration coupons to purchase typewriters, sugar, gasoline, bicycles, footwear, fuel oil, silk, nylon, coffee, stoves, shoes, meat, cheese, butter, margarine, canned foods, dried fruits, jam, and many other items. Some items—like new automobiles and appliances—were no longer made. The rationing system did not apply to used goods (like clothes or cars). The ration system was complex and confusing, but
Item response theory they contribute greatly but over a narrow range. Less discriminating items provide less information but over a wider range. Plots of item information can be used to see how much information an item contributes and to what portion of the scale score range. Because of local independence, item information functions are additive. Thus, the test information function is simply the sum of the information functions of the items on the exam. Using this property with a large item bank, test information functions can be shaped to control measurement error very precisely. Characterizing the accuracy of test scores is perhaps the