1. Statistics Through Applications
How Do We Get “Good” Data?

3. Good Data isn't Based on an Anecdote
Using anecdotal evidence is relying on an isolated example or experience to make a decision
Good data should come from many varied examples and be non-partial
Anecdotes usually appeal to our emotions and fool us into belief while statistics are dry but much more reliable

4. Good Data is Compared Fairly
Often a rate expressed as a percent or fraction is a more valid measure than a simple count of occurrences
Two schools both had 1900 students pass TAKS. One school has 2000 students and the other has Did they perform equally as well?

5. Good Data needs to be Communicated and Read Carefully
An advertisement for a home security system says, “When you go on vacation, burglars go to work. According to FBI statistics, over 26% of home burglaries take place between Memorial Day and Labor Day. Beware - summertime is burglary time!”
Only one in two cameras is actually in operation, but this could soon increase to as many as one in three.Watford Observer, 2 August 2002
Continental Airlines once advertised that it had “decreased lost baggage by 100% in the past six months.”

6. Results from a Gallup poll, taken May 29-31, 2009, with a 3% margin of error.
Can we conclude that more Americans have a favorable impression of Dick Cheney than Nancy Pelosi?
What can we conclude from these graphs?

7. Good Data is Valid, Unbiased & Reliable
Valid – relevant and appropriate
Unbiased – not consistently different from  actuality in one direction
Reliable – as little variation as possible

8. Even Good Data Varies How Long is a Minute?
How accurate are you and your classmates at knowing how long a minute is?
Get a partner and a stopwatch. You will take turns timing and guessing. Using the stopwatch, the timer tells the guesser when to start. When the guesser believes that a minute has passed, he says “Stop.” At that point, the timer stops the stopwatch and records the time that passed to the nearest tenth of a second. Do not tell your partner how much time actually passed!
Reset the stopwatch and switch roles. Continue timing and measuring until each person has been timed three times.

9. Analyzing How Long is a Minute?
Was your data valid?
Was either partner’s data biased?
Which partner was more reliable?
How about the class as a whole? Add your data (3 from each of you) to the class list and graph.
Then figure the average of your 3 measurements and add it to the other graph.

10. All data varies, but we can use Averages to Improve Reliability
No measuring process is perfectly reliable.
The average of several repeated measurements of the same individual is
more reliable (and less variable) than a single measurement.

11. Goal: The least amount of variability and bias possible!

12. How do we achieve our goal?
To reduce bias, use random sampling. A random sample should represent the population, and therefore give unbiased results.
To reduce variability, use a larger sample. Increasing the sample size will almost always give an average estimate that is close to the truth.

13. Good Data shouldn't be confounding
Just because two variables have a relationship, that doesn’t mean one causes the other. There could be a confounding variable at play.
A confounding variable is an additional variable that effects the response but isn't separated out.
Confounding variables are most often found in observational studies comparing a characteristic of two groups or poorly designed experiments .
Sometimes the media ignores confounding variables and misinterprets results from observational studies reporting “proven” links when in statistics we only have shown evidence of a relationship.

14. Consider this data – is there a relationship?
Year
Number of Methodist Ministers in New England
Cuban Rum Imported to Boston (in barrels)
1860 63
8,376
1865 48
6,406
1870 53
7,005
1875 64
8,486
1880 72
9,595
1885 80
10,643
1890 85
11,265
1895 76
10,071
1900
10,547
1905 83
11,008
1910
105
13,885
1915
140
18,559
1920
175
23,024
1925
183
24,185
1930
192
25,434
1935
221
29,238
1940
262
34,705

15. Another confounding example
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?
No, since the children were not randomly assigned to get vaccinations or not, there could be another confounding variable at play.  Perhaps the parents that chose vaccinations also made some other choice that increased the risk of austism or were genetically inclined to have a higher risk of autistic children