1. Day 24 AGENDA:
Answers will be posted on blog.

2. AP STAT Section 5.1: Designing Samples
EQ: What are sampling designs and how can bias occur in these designs?

3. Part I: An introduction to experimental design:
VIDEO 1
VIDEO 2
VIDEO 3

4. Population --- all members of a defined
group that we are studying or collecting
information on for data driven decisions.

5. Sample --- part of the population, a slice of it, and all its characteristics.

8. Ex . Population vs. Sample
A sociologist wants to know the opinions of employed adult women about government funding for day care. She obtains a list of 520 members of a local business and professional women’s club and mails a questionnaire to 100 of these women selected at random. Only 48 questionnaires are returned.
What is the population? What is the sample?
Population is employed adult women.
Sampling Population is 520 members of a local business and professional women’s club.
Sample is the 100 women who received the questionnaire.

9. no treatment treatment imposed surveys cause and effect established
Observation vs Experiment
no treatment
treatment imposed
surveys
cause and effect
established
when experiment
is not practical

10. random digit table flip a coin roll a die
Randomized Experiment --- assignment of treatments controlled by chance:
random digit
table
flip a coin
roll a die

11. Ex. Decide if each of the following is an observation or an experiment
Ex. Decide if each of the following is an observation or an experiment. Explain.
1. You find 100 women age 20 who do not currently smoke. You randomly assign 50 of the 100 women to a group that will smoke a pack of cigarettes a day for 10 years and the remaining 50 women to a group that will remain smoke-free for 10 years. After 10 years, you measure the lung capacity of all 100 women, analyze, interpret, and draw conclusions from your results.
Experiment --- treatment (explain ) was imposed

12. Observation --- no treatment (explain) was imposed
2. You find 100 women age 30 of which 50 have been smoking a pack of cigarettes a day for 10 years while the other 50 have been smoke free for 10 years. You measure the lung capacity of all 100 women, analyze, interpret, and draw conclusions from your results.
Observation --- no treatment (explain) was imposed
3. A group of 60 exercisers are classified as “walkers” or “runners”. A longitudinal study (one conducted over time) is conducted to see if there are differences between the groups in terms of their scores on a wellness exam.
Observation --- no treatment (explain) was imposed

13. Experiment --- treatment (explain ) was imposed
4. A group of 60 volunteers who do not exercise are randomly assigned a fitness program. One group of 30 is enrolled in a daily walking program and the other group is put into a running program. After a period of time, the two groups are compared based on their scores on a wellness index.
Experiment --- treatment (explain ) was imposed

14. Now you decide whether you think the 3 videos we watched at the beginning of class were observations or experiments.
Recycle Bottles Game
Trashcan with Noise
Piano Stairs

15. Steps for Planning A Study
Step 1: Identify population
Step 2: Compile list of subjects in the population from which the sample will be taken
This is called the sampling frame.

16. Step 3: Specify a method for selecting subjects from the sampling frame
Step 4: Select subjects, gather and compile data
Step 5: Make inference about population based on statistics

17. Data Collection Strategies
Census ---  is the procedure of systematically acquiring and recording information about the members of a given population. It is a regularly occurring and official count of a particular population
Sampling --- study a part to learn about the whole

18. Good Data Sampling Techniques Simple Random Sample
--- select individuals at random without replacement; every possible sample of size n has the same chance of occurring

19. Sampling Techniques
Bad Data
1) Voluntary Sampling
--- you choose to
participate
2) Convenience Sampling
--- people chosen based on convenience of contacting them
3) Quota Sampling
--- organized around
categories

20. Ex . What type of sampling does each of the following methods represent?
1. The owner of a club with 1,000 members wants to survey 50 members about the friendliness of the staff. He asks the first 50 members who enter the club one morning.
Convenience--- surveyor asks first 50 patrons to the club on a given day

21. 2. The owner of a club with 1,000 members wants to survey 50 members about the friendliness of the staff. He leaves a stack of response cards by the sign-in desk asking members to participate.
Voluntary--- responders given choice to fill out survey forms

22. 3. The owner of a club with 1,000 members wants to survey 50 members about the friendliness of the staff. He puts each name on a slip of paper then places all of the slips in a hat and mixes them well. He draws one slip out, notes the name, and returns the paper back into the hat. He continues picking and noting the name until 50 different names are selected.
SRS --- every sample of club members size n = 1 has an equal chance of being surveyed

23. Three Types of Bias Which Could Occur in Sample Surveys:
Bias --- systematic error, favors certain outcomes
Three Types of Bias Which Could Occur in Sample Surveys:
Population Under Represented in Sample:
Under-coverage --- my group is left out
of the sample; not even considered
2. Nonresponse --- group is chosen for the sample can't be reached or refuse to participate

24. Inaccurate Responses Result of:
3. Response Bias --- problems that result from the measurement process; due to wording of question or social desirability (what you think the interviewer wants to hear; particularly if survey not confidential)
Know Difference Between Bad Sampling Techniques (nonprobability methods) and Type of Bias as a result of these methods.

25. In Class Assignment for Part 1:
Complete Handout for Samples
Complete Handout for Bias
HW Assignment for Part 1:
p. 333 – 334 #1 - 8
REVIEW TEST CH. 4
p. 316 – #49, 50 – 54, 57

26. Day 25 Agenda: Quiz 4.1 & 4.2 --- 30 minutes
We are still going to Media Center Tues

27. GOOD Sampling Techniques!!
Part II: Types of Probability Sampling
GOOD Sampling Techniques!!
Random Sampling Schemes:
I. Simple Random Sample
SRS
A. each member of
population equally likely
to be chosen
B. members of the
sample are chosen
independently of one another

28. Selection Method:
Obtain master list (Sampling Frame) of population: telephone numbers, house addresses, census tracts
b)Assign digits to subjects in Sampling Frame; randomly select a sample of size n using:
table of random digits
(ii)random number generator

29. What’s another way you could have numbered these students?
00 to 19
When would it be smart to start with 00 instead of 01?
Allows you to read less digits at the time.
Ex 00 to 99 instead of
001 to 100
Why would you consider
this a simple random sample? 19 06 09 10 16 01 08 20
Thomas
Dixon
Every student (2-digit number) has an equal probability of occurring.
Garris
Glenn
Scott
Alex
Flynn
Young

31. II. Stratified Random Sample:
The researcher divides the entire target population into different subgroups, or strata, and then randomly selects the final subjects proportionally from the different strata.

32. II. Stratified Random Sample:

33. II. Stratified Random Sample:

34. II. Stratified Random Sample:

35. NO OVERLAP BETWEEN STRATA INDIVIDUAL FITS INTO ONLY ONE STRATA.
Common variables to use in defining strata:
gender
race
c) geographic location
NO OVERLAP BETWEEN STRATA
INDIVIDUAL FITS INTO ONLY ONE STRATA.

36. Advantages of using strata sampling:
natural strata can simplify fieldwork
b) similar behavior patterns within homogenous groups results in reduction on the error of estimation
c) estimates of population parameters may be desired for subgroups

37. II. Cluster Sampling:
Entire population is divided into groups, or clusters, and a random sample of these clusters are selected. All observations in the selected clusters are included in the sample.

38. II. Cluster Sampling:

39. REMEMBER: The key is you are randomly selecting entire groups.
Common Cluster Sampling Groups:
household
geographic location
c) city block
REMEMBER: The key is you are randomly
selecting entire groups.

40. Advantages of Cluster Sampling:
population frame not available or too costly
b) cost of observations directly proportional to distance separating the elements

41. IV. Systematic Sampling:
The elements of the population are put into a list and then every kth element in the list is chosen (systematically) for inclusion in the sample.

42. All Sampling Techniques:
Quota
Voluntary
Assignment: p. 341 – 342 #10, 11, 13, 14
Assignment: p #21, 23, 25, 27, 28, 30

43. In Class Activity: Rolling Down the River
Form groups of 3 to 5 for this activity. No SINGLETONS!
What your group doesn’t finish in class, you will finish for HW. This is to be turned in tomorrow.

44. Farmer wants data that best represents the actual yield, not the best yield, for the field.
Farmer wants to choose method that will result in least amount of variation.

45. Farmer chooses plots easiest (closest to his house) to harvest.X 6
2.05 2 5
6.5 7 9
none 60 6
600
IQR = 7 – 5 - 2
Remember to calculate LF and UF to determine outliers.
LF: 5 – [(1.5)(2)] = 2
UF: 7 – [(1.5)(2)] = 10

46. You could read only 2 digits at the time. HOW?
Consider digits 00 to 99 instead of 001 to 100.
But our field is already numbered so let’s use 001 to 100.
NO, can’t harvest plot more than once.
Continue until you have selected 10 different plots.

48. The plots are stratified based on distance from the river.
#1 to 10 vertically
Yes, a digit represents location in a strata, not in the entire field.

49. HOW MANY DIGITS DO WE NEED TO LOOK AT TO REPRESENT A PLOT?1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10
HOW MANY DIGITS DO WE NEED TO LOOK AT TO REPRESENT A PLOT?
Use 00 to 09
The first plot selected will be for the first strata.
etc..
Line 145

50. All distances from river represented in each strata.
#1 to 10 horizontally
HOW MANY DIGITS DO WE NEED TO LOOK AT TO REPRESENT A PLOT?
Use 00 to 09
etc.
The first plot selected will be for the first strata.