Appropriate Scores in Bio-Assays Using Death-Times and Survivor Symptoms

Death and survival are the most commonly used markers in biological standardization and in evaluation of medical therapy. Numerous methods are available for estimating the parameters of the dosagemortality curve, and the biologist is often in a state of embarrassment of riches in the choice between a dozen well recommended methods to determine his LD50, ED50, TCiD50, or other D50's with which he is concerned. The experimental records of good biologists and clinicians usually contain more information than death or survival of the subjects on given treatments, but either the LD50-fixation of the investigator prevents these data from entering in the evaluating process, or they are left out because no simple method is available to utilize these observations. In many assays, individual deaths have a quantitative connotation in terms of the time period from exposure to the lethal agent until death occurs. Survival has also quantitative aspects such as time of recovery, severity of symptoms at the time when death is no longer expected, etc. Some data may consist mostly of deaths occurring at different times, in other experiments survivors are in excess. In these cases, group mortality percentages are too large or too small, respectively, to be of biometric use. Attempts are then made to find a transformation of death times or survivor symptoms that can be used as response metameter with approximately linear relationship to dose or with approximately normal distribution, or both. However, in such attempts the problem of truncated or censured distribution will sooner or later present itself, leaving the investigator either in uncomfortable indecision or involved in excessive computation.