1. Statistics and Models Section 2.2
Objectives:
Explain how scientists use statistics.
Describe the types of models commonly used by scientists.

2. Important Statistical Terms
Mean = average
Median – middle number
Mode – most frequent number
13, 7, 6, 3, 6: Find the mean, median, and mode.
Distribution – the arrangement of the bars in a bar graph of a population
EX: Size Distribution of Dwarf Wedge Mussels (Fig. 9, p.39)
Normal distribution – bell-shaped curve

3. Size Distribution of Dwarf Wedge Mussels
Chapter 2
Section 2 Statistics and Models
Size Distribution of Dwarf Wedge Mussels

4. Important Statistical Terms (cont.)
Probability – the chance that something will happen
What does a probability of 0.7 tell you?
Importance of sample size
Sample – a representative group
EX: pennies
Exit Slip: Turn this in!
5 numbers with a mean of 12
Find the mode and the median

5. M&M Samples and Population 
Count your total number of M&M’s.
Count by each color.
Combine all data for your group, and add to data table.
Combine all data for the class, and add to the data table.
At what point did the data match the “normal distribution”?

6. M&M’s Color Distribution
# in your package
% of total in package
# in class
% of class total
Brown (30%)
Red (20%)
Blue (10%)
Orange (10%)
Green (10%)
Yellow (20%)

7. Statistics in Everyday Life
“There is a 30% chance of rain today.”
“A study shows that rain levels are 20% below average this year.”
Risk – the probability of an unwanted outcome.
What do you think is the risk of a big oil spill?
The actual biggest cause of oil polluting is ___________.

8. Risk of Being Killed By Lightning
Lightning kills about 80 people each year in the U.S.
The population of the U.S. is about 280 million. (How many 0’s is that?)
What is your chance of being killed by lightning?

9. Models Physical models Graphical models Conceptual models
3-D; can be touched
EX: crash dummies, model airplanes
Graphical models
Maps and charts
Conceptual models
Verbal or graphical explanation of how a system works or is organized
EX: flow chart of the water cycle, atom

10. Conceptual Model of Mercury Contamination
Chapter 2
Section 2 Statistics and Models
Conceptual Model of Mercury Contamination

11. Models (cont.) 4. Mathematical model
Uses equations to represent the way a system or process works
EX: weather models predict rain chances
Exit Slip: Are models always right? Support your answer.