# S3 SAMPLING

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edwinesosa's
version from
2015-05-14 17:51

## Section

Question | Answer |
---|---|

what is a population | A whole set of items that are of interest |

what is a census | every member of population observed |

what is a sample | a small portion of the population is observed |

advantage of a census | accurate |

cons of a census | cost + time + when testing process if for destruction + too much info makes it hard to process |

cons of sample | may not be large enough to give info about small sub groups |

what is simple random sampling | when every other sample of size n has an equal chance of being selected |

what is a sampling frame | a list identifying every single possible sampling unit that could be included in the sample |

pros of simple random sampling | cheap and easy + each unit included only once + a standard formula can be used to analyse the results |

how does a random number sample work | assign each element of the sampling frame a number, and the numbers of the required elements are selected by using random number tables |

pros of random number sampling | numbers are truly random and free from bias + each number has a known equal chance of selection + easy |

cons of random number sampling | not suitable with large population size |

what is lottery sampling | names in a hat |

pros of lottery sampling | tickets drawn at random + easy + each ticket has known chance of selection |

cons of lottery sampling | not suitable with large population + a sampling frame needed |

systematic sampling | the required elements are chosen at regular intervals from a ordered list, with interval being population size/sample size, first item selected is random and less than k |

pros of systematic sampling | can use with large population + simple |

cons of systematic samplong | can introduce bias (k is 12 when sampling months of the year) + only random if ordered list truly random |

stratified sampling | the population is divided into mutually exlusive strata and a random sample is taken from each |

pros of stratified sampling | more accurate estimates than simple random + reflects the population structure |

Quota sampling | the population is divided into groups in terms of gender, class etc. the number of people in each group is set to try and reflect the groups proportion in the whole population. the interviewer selects the actual sampling units |

pros of quota sampling | It enables fieldwork to be done quickly because a representative sample can be achieved with a small sample size + cheap +easy |

cons of quota | not possible to estimate sampling errors + interviewer has to choose the respondants and may not judge characteristics well + non respondents not recorded + can introduce interviewer bias in who is included |

pros of primary data | known collection method + known accuracy + exact data needed collected |

pros secondary | cheap + large amount of data + much of data has been collected for years and can be used to plot trends |

cons secondary | bias not always recognised + may be in a hard to use form |

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