1. Types of Samples

2. Samples Population – the main group or set from which observations or opinions can be made Sample – a small part of a population from which data is collected Example: if we collect data from three random students about Mr. K’s class, those three students would be the sample of the population (Mr. K’s class)

3. Sampling Plans A sampling plan is a strategy for choosing a sample from a population. What sampling plan would be good to find out the opinions of students regarding the food in the cafeteria?

4. Choosing a Sample When choosing a sample, it should be representative of the population. This means the sample must have characteristics similar to those of the populations. Not all samples are representative samples.

5. Types of Samples 4 types of sampling strategies: – Convenience sampling – Systematic sampling – Voluntary-response sampling – Random sampling

6. Convenience Sampling A convenience sample is made up of people that are easy to reach Problem: Conclusions drawn may be one sided due to “convenience” of the people in survey. Example: Surveying people in a library down the street about how many hours a day they read.

7. Systematic Sampling In systematic sampling, a list is created of every member in a population. From the list, a certain number of individuals are selected from the beginning of the list and then the person conducting the survey chooses every nth person on the list thereafter to participate. For example, I can have a list of 1000 people. I will survey the first 50 people and then I will only select every 50 th person thereafter.

8. Voluntary Sampling A voluntary sample is made up of people who self-select, or volunteer, into a survey. Often, these people have a strong interest in the topic of the survey Problem: most volunteers are biased

9. Random Sampling Random Sampling involves sampling a population in which every possible participant has the same probability of being chosen. Choosing participants randomly where everyone has the same chance of being picked. Example: If I put all your names in a hat to choose from, you all have the same chance of being picked. This is an example of random sampling.

10. Homework Page 45, #1-4