# 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
*n*is sample size*N*is the population size - The number of samples that can be drawn in case of sampling with replacement is
*N*^{n} - The number of samples that can be drawn in case of sampling without replacement is
^{N}C_{n} - There are three different methods of sampling. They are:
- Probability sampling methods
- Simple random sampling
- Stratified sampling
- Multi-stage sampling
- Systematic sampling

- Non probabilistic or non-random sampling methods
- 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