1. Annoucements Exam 1 next Wednesday in both lecture & lab
Pt 1: In lecture: closed book, scantron – bring #2 pencil & know your Univ. ID#
Pt 2: In labs: open book, open notes (no collaboration though)
Annoucements

2. Inferential statistics
Where does “probability” fit in?
Population
Randomness in sampling leads to variability in sampling error
“Randomness” in short run is unpredictable but in long run is predictable
Allows predictions about likelihood of getting particular samples
Lots of samples n=5
Possible Samples
Inferential statistics

3. Basics of probability: Derived from games with all outcomes known
Draw lettered tiles from bag
Bag contains:
A’s B’s and C’s.
Both upper and lower case letters A a b B c C
What’s the probability of getting an A (upper or lower case)?
Total number of outcomes classified as A
Prob. of A = p(A) =
= ??
Total number of possible outcomes
(Sample space)
Basics of probability: Derived from games with all outcomes known

4. What’s the probability of getting an A (upper or lower case) on the first pick and another on a second pick? A a b B c C
1/6
2/6 on 1st pick + a
First Pick:
Prob. of A = p(A) =
2/6 = 0.33 A
Second Pick: ? – it depends on how you sample
Sampling with replacement
Sampling without replacement
The probabilities of selecting the titles change from 1st to 2nd pick A a b B c C a b B c C A b B c C
2/6
1/5
1/5
Basics of probability

5. What’s the probability of getting an A (upper or lower case) on the first pick and another on a second pick? A a b B c C
Sampling with replacement
Sampling without replacement
Probability? a A b B c C
30 total outcomes
2 outcomes of 2 A’s
1st picks
2nd picks
1st picks
2nd picks a a A b B c C A a A b B c C b a A b B c C B a A b B c C c a A b B c C C a A b B c C
36 total outcomes
4 outcomes of 2 A’s
Probability?
Basics of probability

6. Most statistical procedures assume sampling with replacement
For large populations it turns out not to matter much
Example?
Sampling with replacement can also be a disadvantage in experiments –
Why?
Basics of probability

7. The researchers used a questionnaire to interview a random sample of 351 people ages 20 to 80 in the Vancouver, British Columbia, area, asking about their dog ownership and level of physical activity.
Dog owners walked almost twice as many minutes per week as people who did not own dogs, and the dog owners spent more time in all forms of mild and moderate physical activity.
Neither the sex of the owner nor the size of the dog made a difference: men and women who owned dogs participated in increased amounts of moderate exercise compared with those who had no dog. But no statistically significant difference between the two groups was evident in the amount of strenuous exercise performed.
The authors concede that the study, published in the February issue of The American Journal of Preventive Medicine, does not determine whether owning a dog itself makes people exercise more.
Shane Brown, the study's lead author and a graduate student at the Behavioral Medicine Laboratory of the University of Victoria, called this "the million-dollar question."
When the researchers subtracted the time spent walking the dog from total physical activity, dog owners actually walked less than their counterparts without dogs.
This, the researchers say, may suggest that the dog makes the difference. When dog owners choose to engage in moderate physical exercise, the reason may be that a four-legged member of the household is insisting on a walk. Now.
People who own dogs appear to get more exercise than those who do not …
Report (NY Times 2006): dog a more reliable exercise partner than a human.
In the news

8. In the news Research process Variables Variables Ask research question
Identify variables & formulate hypothesis
Define your population
Select a research methodology
Collect your data from a sample
Analyze your data
Draw conclusions based on your data
Repeat
Variables
Operational level
Conceptual level
Regimens: Pounding the Pavement, Stopping at Fire Hydrants
Variables
Independent (explanatory) variables
Dependent (response) variable
Control variables
Random variables
Confound variables
The researchers …, asking about their dog ownership and level of physical activity.
Methods
…. Questionnaires were mailed out in 2004 to collect information about demographics, dog ownership, leisure-time walking, physical activity levels, and theory of planned behavior (TPB) constructs.
In the news

9. In the news Research process Scales of measurement
Ask research question
Identify variables & formulate hypothesis
Define your population
Select a research methodology
Collect your data from a sample
Analyze your data
Draw conclusions based on data
Repeat
Regimens: Pounding the Pavement, Stopping at Fire Hydrants
Instrument used?
Scales of measurement
Nominal
Ordinal
Interval
Ratio
The researchers …, asking about their dog ownership and level of physical activity.
Methods
…. Questionnaires were mailed out in 2004 to collect information about demographics, dog ownership, leisure-time walking, physical activity levels, and theory of planned behavior (TPB) constructs.
In the news

10. In the news Research process Ask the research question
Identify variables & formulate hypothesis
Define population
Select research methodology
Collect data from sample
Analyze data
Draw conclusions based on data
Repeat
Is the sample representative?
Is there bias in sample?
Regimens: Pounding the Pavement, Stopping at Fire Hydrants
The researchers used a questionnaire to interview a random sample of 351 people ages 20 to 80 in the Vancouver, British Columbia, area, (i.e., mailed out questionnaires)
Was it simple random sampling?
Stratified random sampling?
Etc.?
In the news

11. In the news Research process Causal Claims?? Which Research Method??
Ask research question
Identify variables & formulate hypothesis
Define population
Select research methodology
Collect data from sample
Analyze your data
Draw conclusions based on your data
Repeat
Regimens: Pounding the Pavement, Stopping at Fire Hydrants
Causal Claims??
The researchers used a questionnaire to interview a random sample of 351 people ages 20 to 80 in the Vancouver, British Columbia, area,
Which Research Method??
Observational study
Experimental methodology
Quasi-experimental methodology
The authors concede that the study… does not determine whether owning a dog itself makes people exercise more.
This may suggest that .. when dog owners choose to engage in moderate physical exercise, the reason may be that [the dog] is insisting on a walk.
In the news

12. In the news Research process Possible confounds?
Ask research question
Identify variables & formulate hypothesis
Define population
Select research methodology
Collect data from sample
Analyze your data
Draw conclusions based on your data
Repeat
Regimens: Pounding the Pavement, Stopping at Fire Hydrants
Possible confounds?
Threats to internal validity?
If follow-up experiment were designed, what would you do?
In the news

13. Reviewing Producing Data
Scientific method
Research methods
Observation methods
Experimental methods
Quasi-experimental (see Course Packet)
Pop vs. Sample
Variables
Types
Operational definitions
Measurements
Continuous and discrete
Scales of measurement
Errors in Measurement
Validity & Reliability
Dartboard example
Improving validity
Matching design (see CP)
Double-blind design (CP)
Block design (CP)
Sampling
Sampling error
Statistics and parameters
Sampling Methods
Probability Sampling (3 types)
Non-probability Sampling (2 types)
Basic probability
Reviewing Producing Data