1. Unit 1 Day 5: Parameter vs. Statistic

2. Population vs. Sample
A population includes all of the elements from a set of data.
Ex: All the students at PHCS.
A sample consists of one or more observations from the population.
Ex: All the students taking Math III Honors

3. Parameter vs. Statistic
Parameter: a value that represents a population
Statistic: a value that represents a sample

4. Difference Between a Statistic and Parameter
A statistic and a parameter are very similar. They are both descriptions of groups, like “50% of dog owners prefer X Brand dog food.” The difference between a statistic and a parameter is that statistics describe a sample. A parameter describes an entire population.
An article that appears in any publication or in any site on the web may not specifically state whether or not particular data is a parameter or a statistic.
The steps described in the following slide are recommended when considering whether data is a parameter or a statistic.

5. Steps to tell the difference between a statistic and a parameter:
Step 1: Ask yourself, is this a fact about the whole population? With small populations, you usually have a parameter because the groups are small enough to measure: 10% of US senators voted for a particular measure. There are only 100 US Senators, you can count what every single one of them voted.

6. Step 2: Ask yourself, is this obviously a fact about a very large population? If it is, you have a statistic. 60% of US residents agree with the latest health care proposal, researchers have taken a sample to calculate the rest, so it’s a statistic. It’s not possible to actually ask hundreds of millions of people whether they agree.

7. Statistic vs. Parameter Symbols
The symbols change as you move from a statistic to a parameter…Greek symbols are used for parameters.

8. Variable
A variable is any characteristics, number, or quantity that can be measured or counted. A variable may also be called a data item.
Age, sex, business income and expenses, country of birth, capital expenditure, class grades, eye color and vehicle type are examples of variables.
It is called a variable because the value may vary between data units in a population, and may change in value over time. 

9. For the study described, identify the population and the sample
Harris Interactive surveyed 2435 U.S. adults nationwide and asked them to rate quality of American public schools.
Population ~ ALL US ADULTS
Sample ~ 2435 US adults surveyed

10. Let’s Practice
Identify whether the numbers Identified are Statistics or Parameters.
Of all US Kindergarten teachers, 32% say that knowing the alphabet is an essential skill.
b) Of the 800 US Kindergarten teachers polled, 24% say that knowing the alphabet is an essential skill.

11. Of the US population, 36% has an allergy
Of the US population, 36% has an allergy. A sample of 1200 randomly selected adults resulted in 33.2% reporting an allergy. a. Describe the population. b. What is the sample? c. Describe the variable. d. Describe the statistic and give its value. e. Identify the parameter and give its value.

12. Let’s Practice Answers
#1 a) Parameter ~ all kindergarten teachers b)Statistic ~ only a sample of 800 teachers #2 a) Population – all US adults b) Sample – 1200 adults selected c)Variable – Do you have an allergy? Yes or No. d)Statistic – 33.2% (sample value) e) Parameter – 36% (population value)

13. Classwork - In Packet Homework – In Packet