Let the number of individuals in the group be
ordinary
If samples are extracted from them one by one, and each individual is extracted at a time.
The probability of being drawn is equal, so this sampling is called simple random sampling.
Simple random sampling is an indispensable basis for systematic sampling and stratified sampling. There are two common methods to realize simple random sampling:
Draw lots and random number table method. In the process of drawing samples by lot, the chances of each individual being drawn are equal, which is the same.
The key premise of whether this sample is representative or not. Without equal opportunities for each individual, there will be no fairness and rationality of the sample.
In the process of sampling by random number table method, just like sampling by signature method,
The key is to ensure that every remaining individual is drawn.
Will be equal, which requires: the random number table is indeed randomly generated, excluding human factors; Select the start bit in the random number table.
When setting the direction, we must also ensure randomness. If we use the random number table after reading it, the sampled samples will lose fairness, that is,
It has no practical significance.
For simple random sampling, we need to pay attention to: ① it is a non-return sampling; (2) extracting one by one; This is a personal opportunity.
Equal sampling; ④ Simple random sampling is suitable for cases where there are not many individuals in the group. Many people in life use lottery tickets or similar lottery tickets.
Legal cases, such as lottery, telephone number lottery in TV programs, tax voucher lottery, etc. , sampling should also prevent specious situation.
Sampling methods, such as going to star-rated hotels to investigate the income of guests to infer the per capita income of the region, or every other week to a certain week.
Investigate the local traffic flow at intersections and so on.