Sampling Design

1. Sampling Design

2. But First a Sampling Experiment Each group of students should:1. Pull 5 candies out of the bag2. Weigh the candies3. Write down the weight4. Put the candies back in the bag!!5. Pass the scale and bag to your neighbors6. Silently multiply the weight of the 5 candies by 20.

3. No Scale

4. Discussion

5. Definitions • Sampling • procedure involving parts of the whole population • Sample • a subset of the pop. • Population • finite group of elements • Universe • infinite group of elements

6. Why Sample? • Pragmatic reasons • Cheaper • Easier • Faster • Accurate and reliable results • Census?

7. Sampling • Define the target population • A sampling frame • Mailing lists • Reverse directories • lists streets and the people that live on them • Sampling frame error when the entire population is not represented in the sampling frame • Sampling unit- Single  

9. Random Sampling Error vs. Nonsampling (Systematic) Error • Random Sampling Error • The difference between the sample results and the results of a census using the same methods • Systematic error • errors that are not due to chance fluctuations. Sampling frame error is a systematic error.

10. Probability vs. Non-probability sampling • Nonprobability- the probability of any particular member of the population being chosen is unknown. • Therefore there are no appropriate statistical techniques for measuring random sampling error from a nonprobability sample. Thus making inference is inappropriate.

11. Non-probability Sampling • Convenience Sampling • do you have a pulse?

12. Non-probability Sampling • Judgment sampling • using your judgment to select the characteristics of interest

13. Non-probability Sampling • Quota sampling • a min number of individuals with a certain characteristic.

14. Non-probability Sampling • Snowball sampling • initial respondents selected with probability methods, and they refer others

15. Probability Sampling • Simple random sampling – • everyone in pop has an equal probability of being selected

16. Probability Sampling • Systematic Sampling- • using every 50th name in a phone book after a random starting point is selected. • Sampling interval- in this case 50 • Periodicity- when the names are not ordered randomly

17. Probability Sampling • Stratified sampling (increase homogeniety within strata, increase heterogeniety between strata) • Proportional vs. disproportional strata • Optimal allocation

18. Probability Sampling • Cluster sampling • Area sample • Multistage area sampling

19. Statistics • When sampling is not simple random sampling the statistics get much harder, ie more complex. • Observations need to be weighted based upon their probability of appearing in the sample.

20. What is the appropriate sample design?

21. But First a Sampling Experiment Each group of students should:1. Pull 5 candies out of the bag2. Weigh the candies3. Write down the weight4. Put the candies back in the bag!!5. Pass the scale and bag to your neighbors6. Silently multiply the weight of the 5 candies by 20.

22. No Scale

23. No Scale

24. No Scale