Ch 3 Concepts+R Flashcards

1
Q

Sample mean or avg is denoted as….

A

x bar (x with line above it)

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2
Q

population mean is denoted as

A

mu

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3
Q

list of #s denoted as….

A

x_1,x_2,…..,x_n

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4
Q

summation notation

A

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

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5
Q

Little n vs big N

A

n=sample size, N=pop size

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6
Q

Mean, if sample would be…..(equation)

A

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

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7
Q

Mean if population would be…..(equation)

A

mu=(x_1+x_2…..+x_n)/N=(summation)/N

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8
Q

When can mean value be used?

A

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

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9
Q

Sample means used to…..

A

estimate population means (larger sample, better estimate)

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10
Q

Median is

A

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

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11
Q

Advantage of median compared to mean

A

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

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12
Q

mode

A

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

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13
Q

Range

A

difference between largest value and smallest value

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14
Q

Variance

A

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

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15
Q

population variance is denoted by….

A

sigma squared

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16
Q

population variance formula

A

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

16
Q

Sample variance is denoted by….

16
Q

sample variance formula

A

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

17
Q

R-Var command in R finds….

A

unbiased sample variance

18
Q

sample standard deviation (s) is the…

A

square root of sample variance

19
Q

population standard deviation (sigma) is the…

A

square root of population variance

20
Q

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

A

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

21
Q

Z-scores tells us…

A

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

22
Q

z-score equation

A

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

23
Z-score can be_____ but sd is _______
negative, positive
24
Quartile 1
a # larger than 25% at all values but smaller than 75% (ls, sl------let's silly)
25
Quartiles 2
median
26
Quartile 3
a # smaller than 25% all of the values but greater than 75% of all values (sl, ls)-sillies
27
Is there a difference between R code quartile and hand counted?
Yes, due to different algorithm it uses
28
Percentiles
generalization of quartiles (1 to 99)
29
Outliers and 2 types
values larger or smaller than majority (correct values or error) (ex, Elon Musk's salary vs typo)
30
Inter quartile range (IQR)
Q3-Q1
31
Formulas that determine outliers
Q1-1.5IQR Q3+1.5IQR
32