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## PowerPoint Slideshow about ' Statistics!' - daw

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Presentation Transcript

Today

- Check in
- How is that proposal coming along…?

- Finish up material from Tuesday
- Statistics

Statistics

- Purpose for today and Tuesday
- Familiarize you with statistical terms and concepts
- Help you get a general sense of statistics
- What are they?
- Why do we use them?
- What are some basic statistics?

What are they

- Statistics are numbers that describe a sample
- Parameters are numbers that describe a population

What are statistics for?

- We use them to describe our variables
- Descriptive statistics

- We use them to make inferences from samples to populations
- Inferential statistics

- This is why sampling and bias are so very important

Basic descriptive statistics-frequencies

- Frequencies
- Remember: variables are divided into categories
- Frequencies tell us how many are in each type of category
- Frequencies can refer to the raw number, or the percent

Types of variables

- Nominal
- Ordinal
- Interval
- Ratio

Nominal

- “named” variables
- Can be represented with numbers but have no numerical qualities
- There is no rank order

- E.g. Red, blue, green cars
- Male/female gender

Ordinal

- Variables that have “order”
- We assign them a rank, and may use numbers
- We don’t actually know how much the ranks differ
- E.g. bad, worse, worst
- Some of the time, most of the time, all of the time

Ordinal

- We should not manipulate ordinal variables numerically
- Add, subtract, multiply

- Because we don’t know if the categories are exact
- But in practice ordinal variables are numerically manipulated all the time

Interval

- Interval data is rank ordered
- We know that the space from one to the next is “equal”
- E.g. temperature
- But interval data has “no true zero”
- There can’t be a true absence of the thing being measured

- Like temperature, zero is “arbitrary”
- We decide what zero is

Ratio Data

- Like interval data
- It is ordered
- We know that the space from one rating to the next is “equal”
- It has a “true zero”
- There CAN be an absence of it
- E.g. length, weight
- You can have “zero” weight

Useful terms

- Univariate—referring to a single variable
- Bivariate—two variables
- Multivariate—more than two variables
- Proportion—a percent

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