1. Define Population.
In a statistical enquiry, all the items, which fall within the purview of enquiry, are known as population or universe. The population is a complete set of all possible observations of the type which is to be investigated.
2. Define finite and infinite population with examples.
A population is said to be finite if it consists of finite number of units. Number of workers in a factory, production of articles in  particular day for a company are examples of finite population. The total number of units in a population is called population size. A population is said to be infinite if it has infinite number of units. For example the number of stars in the sky, the number of people seeing the Television programmes etc.
3. Write the merits and limitations of census method.
Merits :
The data are collected from each and every item of the population.
The results are more accurate and reliable, because every item of the universe is required.
Intensive study is possible.
The data collected may be used for various surveys, analyses etc.
Limitations :
It requires a large number of enumerators and it is a costly method.
It requires more money, labour, time energy etc.
It is not possible in some circumstances where the universe is infinite.
4. Define Sample.
A finite subset of statistical individuals defined in a population is called a sample.
5. What are the reasons for selecting a sample?
Complete enumerations are practically impossible when the population is infinite.
When the results are required in a short time.
When the area of survey is wide.
When resources for surveys are limited particularly in respect of money and trained persons.
When the item or unit is destroyed under investigation.
6. State the principles of sampling.
Principle of statistical regularity : A moderately large number of units chosen at random from a large group are almost sure on the average to possess the characteristics of the large group.
Principle of Inertia of large numbers : Other things being equal, as the sample size increases, the results tend to be more accurate and reliable.
Principle of Validity : This states that the sampling methods provide valid estimates about the population units (parameters).
Principle of Optimisation : This principle takes into account the desirability of obtaining a sampling design which gives optimum results. This minimizes the risk or loss of the sampling design. The foremost purpose of sampling is to gather maximum information about the population under consideration at minimum cost, time and human power. This is best achieved when the sample contains all the properties of the population.
7. Write the advantages and limitation of sampling.
There are many advantages of sampling methods over census method. They are as follows:
Sampling saves time and labour.
It results in reduction of cost in terms of money and man-hour.
Sampling ends up with greater accuracy of results.
It has greater adaptability.
If  has greater scope.
If the population is too large, or hypothetical or destroyable sampling is the only method to be used. The limitations of sampling are given below:
       1. Sampling is to be done by qualified and experienced persons. Otherwise, the information will be unbelievable.
       2. Sample method may give the extreme values sometimes instead of the mixed values.
       3. There is the possibility of sampling errors. Census survey is free from sampling error.
8. Write the types of stratified sampling.
There are two types of stratified sampling. They are proportional and non - proportional. In the proportional sampling equal and proportionate of items is large, the sample will have a higher size and vice versa. The population size is denoted by N and the sample size is denoted by ' n ' the sample size is allocated to each stratum in such a way that the sample fractions is a constant for each stratum. That is given by n/N = c. So in this method each stratum is represented according to its size. In non-proportionate sample, equal representation is given to all the sub-strata regardless of their existence in the population.
9. Write the merits and limitations of stratified sampling.
Merits :
It is more representative.
It ensure greater accuracy.
It is easy to administer as the universe is sub-divided.
Greater geographical concentration reduces time and expenses.
When the original population is badly skewed, this method is appropriate.
For non-homogeneous population, it may field good results.
Limitations :
To divide the population into homogeneous strata, it requires more money, time and statistical experience which is a difficult one.
Improper stratification leads to bias, if the different strata overlap such a sample will not be a representative one.
10. Explain systematic sampling.
This method is widely employed because of its ease and convenience. A frequently used method of sampling when a complete list of the population is available is systematic sampling. It is also called Quasi- random sampling. The whole sample selection is based on just a random start. The first unit is selected with the help of random numbers and the rest get selected automatically according to some pre designed pattern is known as systematic sampling.
11. What are the merits and demerits of systematic sampling?
Merits :
This method is simple and convenient.
Time and work is reduced much.
If proper care is taken result will be accurate.
It can be used in infinite population.
Demerits :
Systematic sampling may not present the whole population.
There is a chance of personal bias of the investigators.