Statistics

Question 1

list the 3 reasons why we study statistics

Answer 1

1. objective evaluation of numbers
2. population description
3. estimate unknown value

Question 2

what is breeding value?

Answer 2

the actual genetic worth of an animal

Question 3

what is variation?

Answer 3

the raw material that a breeder has to work with

Question 4

list the 2 kinds of variation

Answer 4

1. discontinuous

2. continuous

Question 5

describe discontinuous variation

Answer 5

involves quaLitative traits, where few, discrete genes determine the phenotype, and the phenotype is not greatly influenced by the environment

Question 6

describe continuous variation

Answer 6

involves quaNtitative traits, or economically important traits, where many genes control the phenotype, which has many small gradations that are almost imperceptible to one another, and are highly complex

Question 7

what does a random sample represent?

Answer 7

inferences from a population

Question 8

what is a population parameter?

Answer 8

a numerical descriptive measure for a population, number that describes a population

Question 9

what is a sample statistic?

Answer 9

numerical descriptive measures for a sample, estimate of population parameter

Question 10

what is central tendency?

Answer 10

the values clustered at the midpoint, thinning out symmetrically toward both extremes

Question 11

what are the 3 measures of central tendency?

Answer 11

1. mean
2. median
3. mode

Question 12

what is the most useful statistic for estimating central tendency of most populations?

Answer 12

mean!

Question 13

describe the formula of mean

Answer 13

the sum of all values divided by the amount of values

Question 14

what is variance?

Answer 14

a measure of the distribution (deviation around the mean)

Question 15

describe the formula for variance

Answer 15

defined as the average squared deviation of observations from their mean

Question 16

list the 4 steps to compute variance

Answer 16

1. subtract the mean from each observation in the sample
2. square results of #1
3. add squared results
4. divide sum by n-1

Question 17

what is standard deviation?

Answer 17

“typical” deviation, in absolute value, of an observation drawn at random from the population from its mean

Question 18

how can standard deviation be used?

Answer 18

to describe variation in a population

Question 19

what does standard deviation help us picture?

Answer 19

how much variation actually exists for a trait

Question 20

what is standard error?

Answer 20

how accurately the mean has been estimated

Question 21

what are correlation and regression? and what are they not?

Answer 21

they are measures of association, NOT predictions

Question 22

what is correlation?

Answer 22

measures the strength of the relationship between 2 variables, a population measure

Question 23

when asking, is one trait of an animal associated with another? what are you referring to?

Answer 23

correlation

Question 24

what does the correlation coefficient measure?

Answer 24

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

Question 25

what is the range of the correlation coefficient?

Answer 25

-1.0 to +1.0

Question 26

what does a correlation of 1.0 indicate?

Answer 26

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

Question 27

what does a significant correlation indicate?

Answer 27

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

Question 28

what unites is correlation measured in?

Answer 28

none, it’s unitless

Question 29

what can’t correlation be used for? why?

Answer 29

to predict the level of one variable based on the second, because there is no basis for cause and effect determination

Question 30

what are the 3 types of correlation?

Answer 30

1. phenotypic correlation
2. genotypic correlation
3. environmental correlation

Question 31

describe phenotypic correlation

Answer 31

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

Question 32

give the variable for phenotypic correlation

Answer 32

rp

Question 33

describe genetic correlation?

Answer 33

measures the strength of relationship between breeding value for one trait and breeding value for another trait

Question 34

give the variable for genetic correlation

Answer 34

rg

Question 35

why is genetic correlation important?

Answer 35

because of the concept of correlated response to selection (selection for one trait leads to selection on another trait)

Question 36

describe environmental correlation

Answer 36

measure of the strength of the relationship between environmental effects

Question 37

give the variable for environmental correlation

Answer 37

re

Question 38

what does regression coefficient measure?

Answer 38

measures the change in Y response per unit change in X

Question 39

how good is regression at predicting values?

Answer 39

the greater the slope, the closer the association between 2 traits

Question 40

what units is regression expressed in?

Answer 40

the original units of measure of the values

Question 41

what is the regression of y on x?

Answer 41

byx

Question 42

of x and y in regression, which is the cause and which is the effect (assumed)?

Answer 42

x is cause, y is effect

Question 43

when is regression used?

Answer 43

when we want to predict the numerical value of one trait from the phenotypic value of another, when it may be difficult or expensive to measure y