1. 5-1 Biostatistics CHS 221 by Dr. WajedHatamleh lecture 7&8 Sampling &Sampling Distributions Dr. wajed Hatamleh

2. 5-2 Learning Objectives Determine when to use sampling instead of a census. Distinguish between random and nonrandom sampling. Decide when and how to use various sampling techniques. Be aware of the different types of error that can occur in a study. Understand the impact of the Central Limit Theorem on statistical analysis. Use the sampling distributions of. x Dr. wajed Hatamleh

3. 5-3 Reasons for Sampling Sampling can save money. Sampling can save time. For given resources, sampling can broaden the scope of the data set. Because the research process is sometimes destructive, the sample can save product. If accessing the population is impossible; sampling is the only option. Dr. wajed Hatamleh

4. 5-4 Random Versus Nonrandom Sampling Random sampling Every unit of the population has the same probability of being included in the sample. A chance mechanism is used in the selection process. Eliminates bias in the selection process Also known as probability sampling Nonrandom Sampling Every unit of the population does not have the same probability of being included in the sample. Open the selection bias Not appropriate data collection methods for most statistical methods Also known as nonprobability sampling Dr. wajed Hatamleh

5. 5-5 Random Sampling Techniques Simple Random Sample Stratified Random Sample Systematic Random Sample Cluster (or Area) Sampling Dr. wajed Hatamleh

6. 5-6 Simple Random Sample Number each frame unit from 1 to N. Use a random number table or a random number generator to select n distinct numbers between 1 and N, inclusively. Easier to perform for small populations Dr. wajed Hatamleh

7. 5-7 Simple Random Sample: Numbered Population Frame 01 Alaska Airlines 02 Alcoa 03 Ashland 04 Bank of America 05 BellSouth 06 Chevron 07 Citigroup 08 Clorox 09 Delta Air Lines 10 Disney 11 DuPont 12 Exxon Mobil 13 General Dynamics 14 General Electric 15 General Mills 16 Halliburton 17 IBM 18 Kellog 19 KMart 20 Lowe’s 21 Lucent 22 Mattel 23 Mead 24 Microsoft 25 Occidental Petroleum 26 JCPenney 27 Procter & Gamble 28 Ryder 29 Sears 30 Time Warner Dr. wajed Hatamleh

8. 5-8 Simple Random Sampling: Random Number Table 9943787961457373755297969390943447531618 5065600127683676688208156800167822458326 8088063171428776683560515702965002645587 8642040853537988945468130912538810474319 6009786436018694775889535994004826830606 5258771965854534683400991997297694815941 8915590553906894863707955470627118264493 N = 30 n = 6 Dr. wajed Hatamleh

9. 5-9 Simple Random Sample: Sample Members 01 Alaska Airlines 02 Alcoa 03 Ashland 04 Bank of America 05 BellSouth 06 Chevron 07 Citigroup 08 Clorox 09 Delta Air Lines 10 Disney 11 DuPont 12 Exxon Mobil 13 General Dynamics 14 General Electric 15 General Mills 16 Halliburton 17 IBM 18 Kellog 19 KMart 20 Lowe’s 21 Lucent 22 Mattel 23 Mead 24 Microsoft 25 Occidental Petroleum 26 JCPenney 27 Procter & Gamble 28 Ryder 29 Sears 30 Time Warner N = 30 n = 6 Dr. wajed Hatamleh

10. 5-10 Stratified Random Sample Population is divided into nonoverlapping subpopulations called strata A random sample is selected from each stratum Potential for reducing sampling error Dr. wajed Hatamleh

11. 5-11 Stratified Random Sample: Population of FM Radio Listeners 20 - 30 years old (homogeneous within) (alike) 30 - 40 years old (homogeneous within) (alike) 40 - 50 years old (homogeneous within) (alike) Hetergeneous (different) between Hetergeneous (different) between Stratified by Age Dr. wajed Hatamleh

12. 5-12 Nonrandom Sampling Convenience Sampling: sample elements are selected for the convenience of the researcher Judgment Sampling: sample elements are selected by the judgment of the researcher Snowball Sampling: survey subjects are selected based on referral from other survey respondents Dr. wajed Hatamleh

13. 5-13 Errors u Data from nonrandom samples are not appropriate for analysis by inferential statistical methods. u Sampling Error occurs when the sample is not representative of the population u Nonsampling Errors Missing Data, Recording, Data Entry, and Analysis Errors Poorly conceived concepts, unclear definitions, and defective questionnaires Response errors occur when people so not know, will not say, or overstate in their answers Dr. wajed Hatamleh

14. 5-14 Sampling Distribution of Proper analysis and interpretation of a sample statistic requires knowledge of its distribution. Process of Inferential Statistics x Dr. wajed Hatamleh

15. 5-15 Distribution of a Small Finite Population Population Histogram 0 1 2 3 52.557.562.567.572.5 Frequency N = 8 54, 55, 59, 63, 68, 69, 70 Dr. wajed Hatamleh

16. 5-16 Sample Space for n = 2 with Replacement SampleMeanSampleMeanSampleMeanSampleMean 1(54,54)54.017(59,54)56.533(64,54)59.049(69,54)61.5 2(54,55)54.518(59,55)57.034(64,55)59.550(69,55)62.0 3(54,59)56.519(59,59)59.035(64,59)61.551(69,59)64.0 4(54,63)58.520(59,63)61.036(64,63)63.552(69,63)66.0 5(54,64)59.021(59,64)61.537(64,64)64.053(69,64)66.5 6(54,68)61.022(59,68)63.538(64,68)66.054(69,68)68.5 7(54,69)61.523(59,69)64.039(64,69)66.555(69,69)69.0 8(54,70)62.024(59,70)64.540(64,70)67.056(69,70)69.5 9(55,54)54.525(63,54)58.541(68,54)61.057(70,54)62.0 10(55,55)55.026(63,55)59.042(68,55)61.558(70,55)62.5 11(55,59)57.027(63,59)61.043(68,59)63.559(70,59)64.5 12(55,63)59.028(63,63)63.044(68,63)65.560(70,63)66.5 13(55,64)59.529(63,64)63.545(68,64)66.061(70,64)67.0 14(55,68)61.530(63,68)65.546(68,68)68.062(70,68)69.0 15(55,69)62.031(63,69)66.047(68,69)68.563(70,69)69.5 16(55,70)62.532(63,70)66.548(68,70)69.064(70,70)70.0 Dr. wajed Hatamleh

17. 5-17 Distribution of the Sample Means Sampling Distribution Histogram 0 5 10 15 20 53.7556.2558.7561.2563.7566.2568.7571.25 Frequency Dr. wajed Hatamleh

18. 5-18 Central Limit Theorem For sufficiently large sample sizes (n  30), the distribution of sample means, is approximately normal; the mean of this distribution is equal to , the population mean; and its standard deviation is it is a standard error (SE), regardless of the shape of the population distribution. x n  Dr. wajed Hatamleh

19. 5-19 Central Limit Theorem Dr. wajed Hatamleh

20. 5-20 Exponential Population n = 2n = 5n = 30 Distribution of Sample Means for Various Sample Sizes Uniform Population n = 2n = 5n = 30 Dr. wajed Hatamleh

21. 5-21 Sampling from a Normal Population The distribution of sample means is normal for any sample size. Dr. wajed Hatamleh

22. 5-22 Z Formula for Sample Means Dr. wajed Hatamleh

23. Given the population of men has normally distributed weights with a mean of 172 lb and a standard deviation of 29 lb, a) if one man is randomly selected, find the probability that his weight is greater than 175 lb. b) if 20 different men are randomly selected, find the probability that their mean weight is greater than 175 lb (so that their total weight exceeds the safe capacity of 3500 pounds). Example – Water Taxi Safety

24. z = 175 – 172 = 0.10 29 a) if one man is randomly selected, find the probability that his weight is greater than 175 lb. Example – cont

25. b) if 20 different men are randomly selected, find the probability that their mean weight is greater than 172 lb. Example – cont z = 175 – 172 = 0.46 29 20

26. b) if 20 different men are randomly selected, their mean weight is greater than 175 lb. P(x > 175) = 0.3228 It is much easier for an individual to deviate from the mean than it is for a group of 20 to deviate from the mean. a) if one man is randomly selected, find the probability that his weight is greater than 175 lb. P(x > 175) = 0.4602 Example - cont