Ch 3 Concepts+R

Question 1

Sample mean or avg is denoted as….

Answer 1

x bar (x with line above it)

Question 2

population mean is denoted as

Answer 2

mu

Question 3

list of #s denoted as….

Answer 3

x_1,x_2,…..,x_n

Question 4

summation notation

Answer 4

summation, i=1 at bottom, to n, x_i=x_1+x_2…..+x_n

Question 5

Little n vs big N

Answer 5

n=sample size, N=pop size

Question 6

Mean, if sample would be…..(equation)

Answer 6

x bar=(x_1+x_2…..+x_n)/n= (summation)/n

Question 7

Mean if population would be…..(equation)

Answer 7

mu=(x_1+x_2…..+x_n)/N=(summation)/N

Question 8

When can mean value be used?

Answer 8

mean score of exam, weighted GPA, miles p/gallon

Question 9

Sample means used to…..

Answer 9

estimate population means (larger sample, better estimate)

Question 10

Median is

Answer 10

the number in the middle ( if numbers even, average mean of two middle numbers)

Question 11

Advantage of median compared to mean

Answer 11

median less sensitive to outliers (robust), mean includes entire dataset (more applicable)

Question 12

mode

Answer 12

value in data set that appears most frequently (applies to both qualitative and quantitative)

Question 13

Range

Answer 13

difference between largest value and smallest value

Question 14

Variance

Answer 14

how far values in data set are away from center (mean)

Question 15

population variance is denoted by….

Answer 15

sigma squared

Question 16

population variance formula

Answer 16

sigma squared=(summation (X_i-mu)^2)/N

Question 16

Sample variance is denoted by….

Answer 16

s^2

Question 16

sample variance formula

Answer 16

s^2=(summation (x_i-x bar)^2/(n-1)

Question 17

R-Var command in R finds….

Answer 17

unbiased sample variance

Question 18

sample standard deviation (s) is the…

Answer 18

square root of sample variance

Question 19

population standard deviation (sigma) is the…

Answer 19

square root of population variance

Question 20

Why do we care about standard deviation when we have variance?

Answer 20

variance has squared units so, so we need the square root of variance to get the same unit

Question 21

Z-scores tells us…

Answer 21

how many standard deviations that value is away from the pop mean

Question 22

z-score equation

Answer 22

(x-mu)/sigma –> (x is the #, mu is the mean, sigma is the sd)

Question 23

Z-score can be_____ but sd is _______

Answer 23

negative, positive

Question 24

Quartile 1

Answer 24

a # larger than 25% at all values but smaller than 75% (ls, sl——let’s silly)

Question 25

Quartiles 2

Answer 25

median

Question 26

Quartile 3

Answer 26

a # smaller than 25% all of the values but greater than 75% of all values (sl, ls)-sillies

Question 27

Is there a difference between R code quartile and hand counted?

Answer 27

Yes, due to different algorithm it uses

Question 28

Percentiles

Answer 28

generalization of quartiles (1 to 99)

Question 29

Outliers and 2 types

Answer 29

values larger or smaller than majority (correct values or error) (ex, Elon Musk’s salary vs typo)

Question 30

Inter quartile range (IQR)

Answer 30

Q3-Q1

Question 31

Formulas that determine outliers

Answer 31

Q1-1.5IQR
Q3+1.5IQR