1. Statistics
The science of collecting, analyzing, and interpreting data.
Planning A Study Using The Statistical Problem Solving Process:
Ask a question of interest
Collect some data
Analyze and describe the data
Make a conclusion, answering the question of interest

2. 2 Types of Studies Observational Study Experimental Study
-Record data observed or surveyed
-No treatments imposed
-Used to describe a group or situation
-Impose treatments on subjects
-Record results and compare groups
-Used to see if the treatments cause a change in the response
Experimental Study

3. Measuring Data from Study Subjects or Experimental Units
Various Variables
Explanatory (independent, x) variable: the treatment in an experiment or group label in an observation (may not exist in observational studies)
Response (dependent, y) variable: the result measured in the end of every experimental and observational study
Confounding variable: a variable that might exist in a study that influences the response but can’t be separated from the explanatory variable

4. Example of confounding
A study sites that a group of children who had certain vaccinations were more likely to develop autism than a group of children who did not receive those same vaccinations. 
Does this mean that vaccinations cause autism?
Explanatory:
Response:
Possible confounding:
Effect of confounding:
Whether or not they were vaccinated
Whether or not they developed autism
Vaccination group could have also given children some new diet or supplement that non-vaccination group didn’t give
Vaccination group’s higher rate of autism may be tied to diet or supplement rather than vaccination

5. Census
The systematical collection of data on every single subject in the population.
When the population is large, it will be time consuming and expensive.
Video on census/American Community Survey use at Target:
Difference between ACS and Current Population Survey:

6. Observational Studies
Subjects are randomly selected and asked questions or observed in a particular setting.
Subjects are not influenced in how they respond.

7. Good Survey Questions Avoid unnecessary complexity to question
Avoid misleading questions
Randomize ordering of questions
Ensure confidentiality
Avoid influencing the subject by tone, appearance, or suggestion
Video 17, start at 4:46, 2.5 min

8. Sources of bias in surveys
If a selection process consistently obtains values too high or too low, then bias exists. Some group may be under (or over) represented.
Response Bias: influencing the response in some way
-Non-response bias: a group is left out because they feel uncomfortable, too busy, etc.
Selection Bias : not randomly selected from the entire population of interest

9. Sampling Vocabulary
Population of Interest the set of people or things you wish to know something about
Sampling frame a list of all subjects from which the sample is taken
What is the difference between the sampling frame and the population of interest?
Sample a portion of the population that is selected to represent the population of interest
Random sampling a way of getting a sample that reduces selection bias
How could we ensure a sample is randomly selected?
When is the sampling frame not the same as the population of interest?

10. Population  Random Selection  Sample

11. Sampling Methods Simple Random Sample (SRS) Stratified Random Sampling
Cluster Sampling
Systematic Sampling
Multi-Stage Sampling
Random Digit Dialing
Self-Selected Sample
Convenience Sample
Judgment Sample
“Quickie Polls”
SRS and Stratified sampling methods are tested on the AP exam.

12. Simple Random Sampling
From the entire population
every unit has the same chance of belonging to the sample
and every possible grouping of specified size has same chance of being selected.
Like drawing names out of a hat

13. Stratified Sample vs. Cluster Sample some from all all from some
1st divide population into groups (strata), then take a Simple Random Sample from each strata
(one or more slips from each hat)
1st divide population into groups (cluster), then randomly select some clusters and sample everyone in that cluster
(all slips from one or two hats)

14. Systematic Sampling Random Digit Dialing
From a list, randomly choose starting point (4th entry), and divide into consecutive segments (every 10 names), then sample at that same point in each segment (4, 14, 24, 34,…)
Sample that approximates a SRS of all households that have telephones with a specific exchange
( )
Pew Research:

15. Samples typically resulting in biased results
Self-Selected Sample--radio station call-in Convenience Sample--surveying folks in a mall who appear willing to talk to you Judgment Sample – surveying those you pick as an “expert” selector “Quickie Polls”--hastily designed, poorly pre-tested, one night survey sample for evening news show

16. Random Number Table
Assign a number label to each unit in the population
Read numbers from table from left to right, starting anywhere. The subjects selected for the sample are those read from the table.
Repeats or those not a part of the list are ignored.

17. Sampling & Lays potato chips
Video 16, start at 6:35, about 2 minutes
Nielsen tv ratings