Correlation

Question 1

What is correlation?

Answer 1

measures strength of relationships between 2 variables; is one trait associated with another?

Question 2

What are examples of correlation?

Answer 2

-Is height at withers in beef cattle associated with
body length?
-Is weight of a dairy cow related to amount of milk
produced?

Question 3

What is correlation represented by?

Answer 3

r

Question 4

What does r measure?

Answer 4

• the degree of association between 2 variables (traits) in a sample from a population
• the degree of tightness of the relationship between 2 traits

Question 5

What range does correlation have?

Answer 5

-1.0 to +1.0 (-0.99 to +0.99)

Question 6

What does a correlation range tell us?

Answer 6

the magnitude of the relationship (high or low) and the direction (positive or negative)

Question 7

What does a correlation of +1.0 indicate?

Answer 7

for each standard unit increase in one variable, there is a standard unit increase in the correlated trait

Question 8

What does a significant correlation mean?

Answer 8

that there is a high probability that there is a real association between the traits

Question 9

What does * next to a correlation number mean?

Answer 9

number has been subject to many tests to see if it is accurate and is 95% of the time (p<0.05)

Question 10

What does ** next to a correlation number mean?

Answer 10

99% accurate

Question 11

Does correlation have a unit?

Answer 11

no it is unitless

Question 12

Can correlation be used to predict the level of one variable based on another?

Answer 12

no

Question 13

Correlation doesn’t equal_____.

Answer 13

causation

Question 14

Why doesn’t correlation show cause and effect?

Answer 14

r provides no evidence as to which variable is the cause and which is the effect

Question 15

Does hip height and weight have a positive or negative correlation?

Answer 15

positive

Question 16

Does milk yield and fat % have a positive or negative correlation?

Answer 16

negative

Question 17

Does weight and heart girth have a positive or negative correlation?

Answer 17

positive

Question 18

Does weaning weight and yearling weight have a positive or negative correlation?

Answer 18

positve

Question 19

Does lean cuts and backfat have a positive or negative correlation?

Answer 19

negative

Question 20

How do you calculate the correlation coefficient?

Answer 20

know formula

Question 21

What does a correlation coefficient of 0.01-0.2 mean?

Answer 21

low correlation

Question 22

What does a correlation coefficient of 0.2-0.4 mean?

Answer 22

moderate/medium correlation

Question 23

What does a correlation coefficient of >0.4 mean?

Answer 23

large correlation

Question 24

What are the most common correlations in animal breeding?

Answer 24

phenotypic, genotypic, and environmental

Question 25

What is phenotypic correlation?

Answer 25

measures the strength of relationship between performance (phenotypic value) in one trait and performance in another trait

Question 26

What is genetic correlation?

Answer 26

measures the strength of relationships between breeding value for one trait and breeding value for the other

Question 27

Why is genetic correlation important?

Answer 27

because of the concept of correlated response to selection

Question 28

What is the concept of correlated response to selection?

Answer 28

select for one trait and get response in another trait that you aren't focusing on

Question 29

What is more important than phenotypic correlation?

Answer 29

genotypic

Question 30

What is an example of correlated response to selection?

Answer 30

as milk yield increases and is selected for, milk fat decreases because (?)

Question 31

What are the reasons for correlated response?

Answer 31

gene linkage, pleiotropy

Question 32

What is pleiotropy?

Answer 32

one gene affects more than one trait

Question 33

Is negative correlation bad?

Answer 33

NO, it just means as one increases the other decreases. It isn't bad just as a positive correlation isn't always good

Question 34

What is environmental correlation?

Answer 34

measure of strength of the relationship between environmental effects

Question 35

What is environmental correlation often used for?

Answer 35

management purposes

Question 36

What is rp (subscript)?

Answer 36

phenotypic correlation

Question 37

What is rg (subscript)?

Answer 37

genotypic correlation

Question 38

What is re (subscript)?

Answer 38

environmental correlation

Question 39

What is regression coefficient?

Answer 39

measures the change in Y response per unit change in X (shows one is cause and one is effect variable)

Question 40

What is the formula for regression?

Answer 40

Y=a+bx

Question 41

What does Ŷ represent?

Answer 41

predicted value of Y

Question 42

What does x represent?

Answer 42

independent (cause) variable; X observation

Question 43

What does "a" represent?

Answer 43

intercept for y axis

Question 44

What does b represent?

Answer 44

regressive coefficient (slope)

Question 45

How is regression coefficient expressed?

Answer 45

within a given range of values, positive or negative

Question 46

What can regression coefficient be used to predict?

Answer 46

one value based on another

Question 47

What does regression coefficient have?

Answer 47

representative units of traits of interest

Question 48

What is Ῡ?

Answer 48

mean of Y observations

Question 49

What does Y represent?

Answer 49

dependent (effect) variable

Question 50

What does Y represent?

Answer 50

dependent (effect) variable

Question 51

What is X (line above)?

Answer 51

mean of X observations

Question 52

What is the equation of a straight line?

Answer 52

Y=a + bx

Question 53

The greater the slope.....

Answer 53

the closer the association between 2 traits

Question 54

b=0 means?

Answer 54

no correlation

Question 55

b=0.7 means?

Answer 55

relatively close association

Question 56

When is correlation not applicable?

Answer 56

outside range of values used

Question 57

How many observations are better for correlation?

Answer 57

more

Question 58

How much degree of variation is better for correlation?

Answer 58

less

Question 59

What is regression?

Answer 59

the average of expected change in variable Y per unit change in X

Question 60

How are X and Y expressed for Regression?

Answer 60

in terms of their original units of measure

Question 61

What is byx (yx are subscript)?

Answer 61

the regression of Y on X

Question 62

What does regression assume?

Answer 62

an assumption of cause and effect

Question 63

What does variation in trait X influence?

Answer 63

variation in trait Y

Question 64

What is the cause and effect in weaning weight of cattle?

Answer 64

age is the cause of variation in weight, weight is the effect

Question 65

When is regression used?

Answer 65

when we want to predict the numerical value of one trait from the phenotypic value of another

Question 66

Is it easy to measure Y directly?

Answer 66

no it may be difficult or expensive

Question 67

Why can selecting for Y be expensive/difficult?

Answer 67

slaughtering best animals to determine qualities (yield grade or cutability of pork carcasses)