# Summary

• Sampling is a process of learning about the population on the basis of samples drawn from it.
• There are four basic principles of sample survey. They are:
• Law of statistical regularity
• Principle of inertia
• Principle of optimization
• Principle of validity
• The deviation between the obtained values of population parameter and its observed values is known as errors.
• There are two types of errors.
• Sampling error
• Non-sampling error
• For sampling with replacement, the standard error is calculated using the formula
• For sampling without replacement, the standard error is calculated using the formula

Where,

s is the standard deviation of the statistic

n is sample size

N is the population size
• The number of samples that can be drawn in case of sampling with replacement is Nn
• The number of samples that can be drawn in case of sampling without replacement is NCn
• There are three different methods of sampling. They are:
• Probability sampling methods

Types of probability sampling methods:
• Simple random sampling
• Stratified sampling
• Multi-stage sampling
• Systematic sampling
• Non probabilistic or non-random sampling methods

Some of the important methods are as follows:
• Judgmental sampling
• Convenience sampling
• Quota sampling
• Mixed sampling
• Statistical inference is that branch of statistics which deals with the theory and techniques of making decisions regarding the statistical nature of the population using samples drawn from the population.
• Statistical inference has two branches. They are:
• Theory of estimation
• Testing of hypotheses
• There are two types of estimation. They are:
• Point estimation
• Interval estimations