Ch 2 Flashcards

1
Q

Percentile

A

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

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2
Q

graph to show percentiles

A

Relative Cumulative Frequency Graph or an Ogive

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3
Q

Standardized score (z-score)

A

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

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4
Q

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

A

how many standard deviations a value is from the mean

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5
Q

Effects of adding (or subtracting) a constant

A

+ 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

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6
Q

effects of multiplying (or dividing) by a constant

A

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

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7
Q

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

A

+ and - doesnt change shape or spread

x & divid. doesnt change shape

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8
Q

Density Curve

A

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

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9
Q

what are density curves like a model of?

A

like a model of a histogram

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10
Q

density curves have an area of exactly ____ underneath it

A

1

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11
Q

median and mean on a density curve?

A

median- divides area under the curve in 1/2

mean- curve would balance if made of solid material

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12
Q

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

A

closer to the tail end (balance point)

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13
Q

Normal curves are what?

A

They are density curves!

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14
Q

Shape of a normal curve

A

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

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15
Q

How are normal curves described?

A

completely described by giving its mean and standard deviation

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16
Q

where is the mean located on a normal curve?

A

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

17
Q

How does a normal curves standard deviation affect its spread?

A

curves with larger standard deviations are more spread out

18
Q

how are normal distributions abbreviated?

A

N( mean , standard deviation )

19
Q

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

A

the empirical rule

20
Q

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

A

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

21
Q

example of a normal distribution?

22
Q

example of not usually a normal distribution

A

income (usually right skewed)

23
Q

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

A

it has to follow to 68-95-99.7 rule

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

24
Q

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

A

80% of the total data is below you

25
what does it mean to have a z-score of .6126
it means that this value is approximately .6126 standard deviations above the mean
26
when to use inverse cdf?
When you know the percent below
27
When to use normal cdf?
when you know the z score and what part of the data youre trying to ifnd