Dose-response studies evaluate the effect of a toxic substance at various doses (on animals or cells). Knowing the LD₅₀ allows us to compare toxics directly— that is, which are more toxic than others. Charting the actual change in effect as the dose increases (the “dose response”) allows us to predict effects at doses other than those tested. We can also determine if there is a threshold of exposure that must be reached before harmful effects are seen.