Ch 2

Question 1

Percentile

Answer 1

the pth percentile of a distribution is the value w/ p percent of the observations less than it (# of people below you divided by the total)
% of ppl below you

Question 2

graph to show percentiles

Answer 2

Relative Cumulative Frequency Graph or an Ogive

Question 3

Standardized score (z-score)

Answer 3

if x is an observation from a distribution that has a known mean and standard deviation, the standardized score for x is
z= (x-mean)/sx

Question 4

what does the z-score (standardized score) tell you?

Answer 4

how many standard deviations a value is from the mean

Question 5

Effects of adding (or subtracting) a constant

Answer 5

+ same positive #a to each observation (or subtracting a from)
+ a to or - a from measure of center and location
does NOT change shape or measures of spread

Question 6

effects of multiplying (or dividing) by a constant

Answer 6

x or dividing each observation by same positive # b
x or divides measures of center and location by b
x or divides measures of spread by b
does NOT change shape of distribution

Question 7

different between x & divid. and + & - by a constant

Answer 7

+ and - doesnt change shape or spread

x & divid. doesnt change shape

Question 8

Density Curve

Answer 8

model of the data (describes the overall pattern of a distribution)

Question 9

what are density curves like a model of?

Answer 9

like a model of a histogram

Question 10

density curves have an area of exactly ____ underneath it

Answer 10

1

Question 11

median and mean on a density curve?

Answer 11

median- divides area under the curve in 1/2

mean- curve would balance if made of solid material

Question 12

if a density curve is skewed, the mean line is _____ compared to the median

Answer 12

closer to the tail end (balance point)

Question 13

Normal curves are what?

Answer 13

They are density curves!

Question 14

Shape of a normal curve

Answer 14

All normal curves have the same overall shape; symmetric, single-peaked, & bell-shaped

Question 15

How are normal curves described?

Answer 15

completely described by giving its mean and standard deviation

Question 16

where is the mean located on a normal curve?

Answer 16

located at the center of the symmetric curve and is the same as the median

Question 17

How does a normal curves standard deviation affect its spread?

Answer 17

curves with larger standard deviations are more spread out

Question 18

how are normal distributions abbreviated?

Answer 18

N( mean , standard deviation )

Question 19

The 68-95-99.7 rule is also called what?

Answer 19

the empirical rule

Question 20

What does the 68-95-99.7 rule tell us?

Answer 20

in a normal distribution approximately…
68% of the observations fall within 1 standard d. of the mean
95% within 2 s.d. of the mean
99.7% within 3 s.d. of the mean

Question 21

example of a normal distribution?

Answer 21

height

Question 22

example of not usually a normal distribution

Answer 22

income (usually right skewed)

Question 23

in order for data to be normal… what does it have to follow? How do you check for this?

Answer 23

it has to follow to 68-95-99.7 rule

Create a NPP, if it is roughly linear, the data is roughly normal

Question 24

if something is in the 80th percentile, what does that mean?

Answer 24

80% of the total data is below you

Question 25

what does it mean to have a z-score of .6126

Answer 25

it means that this value is approximately .6126 standard deviations above the mean

Question 26

when to use inverse cdf?

Answer 26

When you know the percent below

Question 27

When to use normal cdf?

Answer 27

when you know the z score and what part of the data youre trying to ifnd