1. Synthesis and Review for Exam 1
STAT 250
Dr. Kari Lock Morgan
Synthesis and Review for Exam 1

2. EXAM 1 In-class on Wednesday, 2/22
Covers everything we have done in class or lab so far (Chapters 1 – 3 in book, except not 2.6 or 2.7)
Bring a non-cell phone calculator and a one-sided page of notes (8 ½ x 11 paper)
Review reading and optional review problems posted on WileyPlus (doing lots of problems is the best way to study!)
See the Study guide posted on Canvas

3. Exam Topics: Ch 1-3 Chapter 1: Data Collection
Data (cases, variables, etc.)
Sampling
Observational studies and confounding
Randomized experiments
Chapter 2: Descriptive Statistics (except not 2.6)
Summary statistics for one or two variable(s)
Graphical displays for one or two variable(s)
Chapter 3: Confidence Intervals
Sampling distributions
Confidence intervals
Margin of error
Standard error and 95% confidence intervals
Bootstrapping
Percentile method for any level of confidence

4. What happens when you switch to organic food?
Question of the Day
What happens when you switch to organic food?
The Organic Effect: What Happens When you Switch to Organic Food. 9/15/15.

5. The Organic Effect
A study took a Swedish family who ate conventionally (non-organic) and had them eat only organic food for 2 weeks
The resulting video publicizing the study has had over 30 million views between Youtube, Facebook, and other sites
Here we look at data from the original study
Magner, J., Wallberg, P., Sandberg, J., and Cousins, A.P. (2015). Human exposure to pesticides from food: A pilot study. IVL Swedish Environmental Research Institute. January 2015.

6. Data
Measurements on pesticide levels taken the week before switching to organic (while on regular non-organic diet)
Ate only organic for two weeks
Measurements on pesticide levels taken again the second of those two weeks
Explanatory variable: before or after switching to organic food
Response variables:
Pesticide detected or not
Pesticide concentration (μg / g crt)

7. Generalize?
Can we generalize to a population of all people?
Yes No

8. Study Design Is this an experiment or an observational study?

9. Causality?
Can we make conclusions about causality?
Yes No

10. Variables
We first want to analyze detection of pesticides (pesticide detected or not) before and after eating organic. This is a question involving
One categorical variable
Two categorical variables
One quantitative variable
Two quantitative variables
One quantitative and one categorical variable

11. Visualization
In analyzing detection of pesticides (pesticide detected or not) before and after eating organic, how might we visualize this data?
Bar chart
Histogram
Side-by-side boxplots
Side-by-side bar charts
Scatterplot

12. Detection of Pesticides
There were 12 pesticides measured 20 times each, before and after eating organic, yielding 240 measurements in each group.
Before eating organic, 111 measurements detected pesticide.
After eating organic, only 24 measurements detected pesticide.
Create a two-way table summarizing this data.

13. Detection of Pesticides

14. Parameter and Statistic
In analyzing detection of pesticides (pesticide detected or not) before and after eating organic, what would be an appropriate parameter and statistic for inference?
Single proportion
Difference in proportions
Single mean
Difference in means
Correlation

15. Detection of Pesticides
Detected
Not Detected
TOTAL
Before eating organic
111
129
240
After eating organic 24
216
135
345
480
111/135 – 129/345
111/129 – 24/216
111/240 – 24/240

16. Bootstrap Distribution
This is a bootstrap distribution based on simulations. Approximate a 99% confidence interval.
(0.33, 0.4)
(0.3, 0.42)
(0.27, 0.45)
(0.25, 0.5)

17. Interpretation Interpret the confidence interval in context.
We are 99% confident that the proportion of pesticides detected is between 0.27 and higher when eating non-organic food then while eating organic food.
confidence level
parameter defined in context
confidence interval

18. Variables
We’ll next analyze the response variable concentration of pesticide (measured in μg / g creatinine) to see if it differs before and after eating organic. This is a question involving
One categorical variable
Two categorical variables
One quantitative variable
Two quantitative variables
One quantitative and one categorical variable

19. Visualization
In analyzing concentration of pesticides before and after eating organic, how might we visualize this data?
Bar chart
Histogram
Side-by-side boxplots
Side-by-side bar charts
Scatterplot

20. Pesticides

22. Parameter and Statistic
In analyzing pesticide concentration (for any one pesticide) before and after eating organic, what would be an appropriate parameter and statistic for inference?
Single proportion
Difference in proportions
Single mean
Difference in means
Correlation

23. Pesticide
24D
6.46
0.94
5.52
3-PBA
27.05
2.54
24.52
35DC
19.12
0.97
18.15
CCC
179.43
3.68
175.75
ETU
2.90
1.20
1.70
Mepiquat
34.20
5.58
28.62
Propamocarb
2.10
0.24
1.86
TCP
38.83
7.48
31.35
Which one do you want a confidence interval for?

24. 95% Confidence Interval Data
Use bootstrap distribution from StatKey to create a 95% confidence interval using the standard error method.
Interpret the confidence interval in context.

25. Variables
Actually, this data is paired (before and after measurements on the same people), so it makes sense to look at the differences in pesticide concentration, before – after. This is a question involving
One categorical variable
Two categorical variables
One quantitative variable
Two quantitative variables
One quantitative and one categorical variable

26. Visualization
In analyzing the differences in concentration of pesticides before and after eating organic, how might we visualize this data?
Bar chart
Histogram
Side-by-side boxplots
Segmented bar charts
Scatterplot

27. Parameter and Statistic
In analyzing the differences in concentration of each pesticide before and after eating organic, what would be an appropriate parameter and statistic for inference?
Single proportion
Difference in proportions
Single mean
Difference in means
Correlation

28. 3-PBA Insecticide found in grains, fruits, vegetables
Difference in 3-PBA concentration before and after:

29. Bootstrap for 3-PBA
Based on this bootstrap distribution with bootstrap statistics, the standard error is closest to… 1 4 7 10

30. Confidence Interval
Using the statistic and standard error, calculate a 95% confidence interval and interpret in context.

31. How to Study for Statistics?
See the Study guide posted on Canvas

32. To Do
HW 3.3, 3.4 (due Wednesday, 2/22)
STUDY FOR EXAM 1! (2/22)