Introduction

In a certain university, suppose we were to obtain the height, sex, weight, and age of each student in a large class in Biostatistics, then such a collection of numbers or survey represents characteristics of the group of individuals contained in this class. If the aggregate of individuals in this class represents the only individuals of interest in the survey, they constitute the Universe or population of interest. If, however, the Universe is composed of a wider aggregate or group of individuals, say the full time Undergraduate students at this University, then the members of this class represent only a part or sample of the Universe or population. Complete enumeration or survey of a characteristic in the population is defined as a Census whereas enumeration on only a part of the population is known as a Sample or as a Sample Survey. Population or Universe may consist of characteristics of people, or acres in farms, Sex, etc. etc. Examples are—all progeny of a particular rat, the birthweights of pigs in one litter, all possible values of millet yield per acre in Kano State. Populations are classified and described by numbers. Students in this University for example, are described by their registration or matriculation numbers. It is a fact, however, that the more developed a society is, the more that society will be characterized by numbers. Knowledge of characteristics of a society allows intelligent action to be taken in order to further develop the society. A sample on the other hand is a part of the population (in some cases, a sample may include the whole of the population). Often, we are interested as researchers in the behavior of a variate throughout a population, but observations on every member of the population may be impossible. For instance, we cannot contemplate catching and weighing every fish in a particular study pond or counting the number of every deficient seed in a kilogram bag of seeds. Sometimes too, the restriction is stronger than consideration for economy or speed.