AP Stats Unit 1 Exploring One Variable Data

Individuals

objects described by a set of data

Variable

any characteristic of an individual 

categorical variable

descriptive variable

quantitative variable

numerical variable

how to describe distributions

with the mnemonic device SOCS

* **S-** Spread. Give the lowest and highest values of the set
* **O-** Outliers. Are there any values that stand out in the distribution?
* **C-** Center. What is the approximate mean?
* **S-** Spread. Does the graph show symmetry or skew?

Five number summary

Minimum, Q1, Median, Q2, Maximum

How do you find an outlier

1\.5 times IQR (subtract this value from Q1 or add to Q3)

IQR

Q3 minus Q1

Density Curve

Always on or above the horizontal axis

Has an area of 1

median

where the curve would be split to be perfectly in half (resistant to outliers)

mean

where the curve would be perfectly balanced (closer to skew, influenced by outliers)

z-score

how many standard deviations you are away from the mean

Pth percentile

the value such that p percentile fall at our below it

discrete variable

 countable number of values

continuous variable

infinite number of values

how do you find relative frequency

dividing the frequency for each category by the sum of all frequencies

dependent variable

the variables that are being measured or observed in a study.

independent variables

the variables that are being manipulated or controlled in a study.

controlled variables

variables that are kept constant or controlled in a study,

sum of all standard deviations

is equal to zero

when should standard deviation be used

used when the mean is chosen as the measure of center