UNIT 2 VOCAB

Question 1

What does r tell us?

Answer 1

How STRAIGHT a positive or negative relationship is between two QUANTITATIVE variables

Question 2

What values can r be?

Answer 2

from -1 to +1

Question 3

What are some strong r values and some weak r values

Answer 3

Strong r values are close to 1 or -1, like -0.83 or 0.94. Weak r values are close to zero like 0.10 or -0.06

Question 4

What if a scatterplot goes straight across horizontally?

Answer 4

NO ASSOC. That would be like height and IQ. If each height has about the same IQ, then they are INDEPENDENT

Question 5

If something is correlated is it associated?

Answer 5

Yes (if it is straight)

Question 6

association or correlation?

Answer 6

association is talking about a relationship? correlation is an actual calculated number

Question 7

How to describe association on scatterplot?

Answer 7

DIRECTION… FORM.. STRENGTH (and outliers)

Question 8

direction?

Answer 8

positive or negative

Question 9

form?

Answer 9

straight, curved

Question 10

strength?

Answer 10

give the r value (if straight), or say? “tightly packed” or “ loosely packed”

Question 11

does correlation mean causation?

Answer 11

NO WAY DUDE

Question 12

Give example of incorrectly using the word “correlation”

Answer 12

“there is a correlation between gender and video game playing” This person should say “association.” You can’t say correlation because gender is categorical.

Question 13

does high r value mean anything?

Answer 13

An r value alone tells little. CHECK THE SCATTER.. IS IT LINEAR?? make sure it’s linear first.

Question 14

How is r calculated?

Answer 14

r= sum(ZxZy) / (n-1)—- the sum of rectangle areas on standardized axes

Question 15

how can you check for “straight enough?”

Answer 15

residuals plot fool!

Question 16

how do you interpret slope?

Answer 16

for an increas of 1 [unit of x] there is an (increase/decrease) of [SLOPE] [units of y]

Question 17

how do you interpret y intercept?

Answer 17

The model predicts that if there were no [x stuff] this is how much [y stuff] you’d have

Question 18

how to interpret slope EQUATION? rSy/Sx

Answer 18

for each increase of 1 st dev in x direction, you go r st dev in y direction.

Question 19

If r= 0.8.. An x value that is 2 standard deviations above the mean will have a predicted y value that is _______

Answer 19

1.6 standard deviations above the mean

Question 20

if you mult or divide the x’s or y’s (shift/scale) does r change?

Answer 20

no. the strength remains the same. (If you log or square it, it will change, but just adding or multiplying won’t change it)

Question 21

if you switch x and y does r change?

Answer 21

NO. The strength stays the same.

Question 22

if you switch x and y will slope change?

Answer 22

YES- slope is rsy/sx? to get new slope you do: (r sqared)/old slope

Question 23

Can you predict an X by using a Y?

Answer 23

NOT WITH THE SAME EQUATION! BE CAREFUL!! You have to change the entire equation and start from scratch?

Question 24

What point is on every regression line?

Answer 24

the mean-mean point. (x bar, y bar)

Question 25

Why is it calle d "least squares regression line?"

Answer 25

Because, after you find the mean-mean point, you fix the line so that it minimizes the squared vertical distance to that line (minimizes the squared residuals)

Question 26

interpret r squared

Answer 26

r squared % of variability in y can be explained by the model. The rest is in residuals?

Question 27

does high r squared mean a good model?

Answer 27

CHECK STRAIGHNESS FIRST. you should check your plot and residuals to make sure model is appropriate and no outliers present? then it means something

Question 28

is r sensitive to outliers?

Answer 28

yes. A single outlier can make it seem like there is a relationship (out in x direction..), or that there is none.

Question 29

Look for lurking variables?

Answer 29

think hot chocolate sales in caf at wachusett mountain and ski accidents at wachusett mountain. Did the chocolate cause the accident??????

Question 30

outliers in regression?

Answer 30

doesn't follow the "flow" (pinky trick)

Question 31

what about your calculator for using curves to fit curved data?

Answer 31

sure.. Quadreg, cubicreg, lnreg, etc? just be careful when substituting while writing the equation given.

Question 32

what does "regression to the mean" mean?

Answer 32

preditions for y are closer to the mean y (y bar) than the actual x is to the mean x (in s.d). Sons were closer to average height than the dads. Super tall dads had tall sons, but not super tall sons, on average.

Question 33

what does influential mean?

Answer 33

It means that the point, when added or removed to data, will influence the SLOPE.. Generally these are outliers in the x direction?. Far left or right.

Question 34

what is a linear model?

Answer 34

it is an equation you can use? or a line of a graph, but it is just a model that says what kind of happens, and can be used to ESTIMATE WHAT MIGHT HAPPEN

Question 35

what is a residual?

Answer 35

ACTUAL-PREDICTED. A-P. like this class.. AP (get it?)

Question 36

what is b1 and bo ?

Answer 36

b1 is the SLOPE, and bo is the intercept. Remember that bo can be thought of as "b old" it is the old b? the intercept in y=mx+b? so it is still the intercept.

Question 37

what is leverage?

Answer 37

leverage just means it is far away from x-bar? far right or left from the middle.. Some leverage points are not influential if they go along with the flow of the scatter.

Question 38

what is the line that you plot?

Answer 38

IT IS A MODEL!

Question 39

what is the LSRL

Answer 39

the "least squares regression line" that line.. That equation

Question 40

what should we look for in resid plot?

Answer 40

curve or pattern.. Also, it should have equalish scatter from left to right

Question 41

what's up with extrapolation?

Answer 41

not a good idea. sometimes it's all you can do, but still, NOT GOOD

Question 42

which is explanatory variable?

Answer 42

x. horizontal axis. it "explains" what happens to y

Question 43

which is response?

Answer 43

y.. Vertical axis.. It "responds" to the x

Question 44

will residual plots always show outliers? (will outliers always have large residuals?)

Answer 44

Not necessarily.. Some points have so much leverage, they pull the line up to it?

Question 45

What is homoscedasticity?

Answer 45

equal scatter along the regression line

Question 46

What if the scatterplot is curved?

Answer 46

either straighten it and fit a line, or keep it and fit a curve (quadreg, cubicreg, lnreg, logreg)

Question 47

How can you straighten data?

Answer 47

Do stuff to the y (square it, root it, log it, etc) and recheck the plot. Remember to put the transformation into your equation.. Example Sqrt y = 4.33 - 2.03 x

Question 48

How do you undo a log when solving?

Answer 48

10^ stuff

Question 49

How do you undo an ln when solving?

Answer 49

e^stuff

Question 50

How do you undo sqrt when solving?

Answer 50

^2

Question 51

How do you undo squares or cubes?

Answer 51

^ 1/2 or ^ 1/3

Question 52

How do you get equation from computer output?

Answer 52

y= b0 + b1 xy is the dependent variableb0 is the coefficient of constant (or it says intercept)b1 is the coefficient of the variable given (indep)x is the indep variablegenerally arranged: Y= this down plus this left "