is controversy, however, over what happens when researchers take children whose behavior has improved on a diet that eliminates several thousand additives, and then challenge them with one or a few additives, usually synthetic colors. Especially in the early studies, if such a challenge did not produce a change in behavior, researchers often concluded that the diet had not directly caused the initial improvement in behavior. Rather, the assumption was that the improvement had been due to a placebo effect. There are other possible reasons for the failure of a challenge to evoke a response, however. For example, the amount of additive used as a challenge might have been too small to cause an effect. A comparison of studies using food dyes as the challenge indicates that there is likely a dose-related response: when a larger dose of the challenge is used, more children react to it. In addition, the effect of a challenge additive might only be seen in synergy with other additives or foods, or the additive used for the challenge may simply not be among those causing the original effect. more recent findings Recent studies show that between 50% to 85% of children placed on an additive-restricted diet show improvement. For example, in a 1994 study of 200 children, 75% of the children improved on a Feingold-type diet; more than 82% of them got worse in a double-blind challenge using small-to-modest amounts of the single food dye Tartrazine (Yellow #5), and a dose-response effect was observed. In