Random Samples Skill 03

Objectives Know the importance of random samples Describe different kinds of sampling

A simple random sample is a subset (n) of an entire population in which each member has an equal probability of being chosen. It is meant to be an unbiased representation of a population. Example: A group of 25 students chosen out of a hat from the entire school. The population is the entire school The sample is the 25 chosen students The sample is random because each student has an equal chance of being chosen.

Other Sampling Techniques… Stratified Sampling: Divide the entire population into distinct subgroups called strata. The strata are based on specific characteristics such as age, income, educational level and more. All members of stratum share the characteristic. Draw random sample from each stratum. Systematic Sampling: Number all members of a population sequentially. Then, from a starting point selected at random; include every kth member of the population in the sample.

Other Sampling Techniques… Cluster Sampling: Divide the entire population into pre-existing segments or clusters. Make a random selection of clusters. Include every member of each selected cluster in the sample. Multistage Sampling: Use a variety of sampling methods to create successively smaller groups at each stage. The final sample consists of clusters. Convenience Sampling: Create a sample by using data from population members that are readily available.

Example; Sampling USA Today regularly asks readers, “Have a complaint about airline baggage handling, refunds, advertising, customer service? Write; …” What kind of sampling method is this? Explain… Cluster Sampling Are the results likely to be biased? Explain… Yes; only getting opinions of one group/cluster of people

Example; Sampling What type of sampling is the federal government deal with? Stratified sampling; the country is spilt up into divisions of states and districts each group has a vote.

Example; Sampling Suppose you have been hired by a group of all- sports radio stations to determine the age distribution of their listeners. Describe in detail how you would select a random sample of 2,500 people from the 35 listening areas involved. Either cluster or stratified sampling, the stations are split into areas so either would be fair samples.

Skill 03: Random Samples Summarize Notes Read section 1.3 Homework Worksheet