# Chapter 2 Sampling

Sampling is the act of gathering data from a certain population, in order to make prediction about some property of the population of interest. Each time one goes out to the field to sample, one gets different answers for the same set of quantities of interest, making those answers random variables.

For finite population, there are two techniques called

*sampling with replacement*and*sampling without replacement*.Sampling without replacement is sometimes called

*simple random sampling*and one needs to be careful with it. However, if the population size is very very large compared to the sample size (a very subjective judgement), it is common in practice to treat the sampling data as I.I.D. RVs.