Let's assume you are conducting an experiment to determine the effect of a new drug on the incidence of epileptic seizures. You select 20 epileptics from the 150 epileptics being treated at a nearby hospital and administer the drug to them. You record the number of seizures in each of the 20 subjects for one month. Then you record the number of seizures in each of the 20 subjects for one month without the drug. Being compulsive, you also record the number of seizures for the remaining 130 epileptics for one month. The number of seizures for each of the 130 epileptics constitutes

Data collection for the remaining 130 ensures accuracy. it makes the investigator to determine the effects or interaction of the drug( the dependent variable ) in each of the 130.That is how the drug exhibited it effects on epilepsy in wide range of patients, the response of each patients, so that its potency can be determined. if the drug actually have any effect on epilepsy or it was due to some other physiological effects in the subjects. Thus accurate effects of the drug(dependent variable) can be determined from the observation of ranges of data collected .