Basic Statistical Toolbox Flashcards

1
Q

mathematical statistics

A

concerned with theoretical foundations (probability theory)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

applied statistics

A

concerned with modelling of data and the errors in our observations to make inferences about the physical system we are observing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

statistical error

A

Uncertainty in the measurement of a physical quantity that is essentially unpredictable – just
as likely to yield a measurement that is too large as one that is too small.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

‘common sense principle’

A

if we repeat our measurements many times and average the results then average length = ‘true’ length

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

systematic error

A

Uncertainty in the measurement of a physical quantity that is always systematically too large
or too small. (Measurement is biased)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Note that here the systematic error enters not when we make our measurements, but

A

when we analyse them

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Systematic flaws in our data analysis methods, rather than in
our data themselves, are just as serious but

A

easier to fix

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

plausible reasoning

A

probability measures our degree of belief that something is true

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

prob(X)=1

A

certain that X is true

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

prob(X)=0

A

certain that X is false

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

In astronomy we generally measure continuous variables which can
take on

A

infinitely many possible values

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

with infinitely many possible values, p(X) is no longer a probability but a

A

probability density function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

probabilities are never

A

negative
p(x)>or=0 for all x

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

we compute probabilities by

A

measuring the area under the pdf curve

ie integral between a and b of p(x) dx

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

normalisation

A

integral between -infinity and infinity =1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

important pdfs:

A
  1. poisson
  2. uniform
  3. central/normal/gaussian
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

examples of poisson pdfs

A

number of photons counted by CCD
number of galaxies counted by galaxy survey
photons in laser beam

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

poisson pdf assumes

A

detections are independent and there is a constant rate μ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

uniform pdf

A

p(x)=1/b-a when a<x<b
o otherwise

20
Q

what is a cdf

A

cumulative distribution function

21
Q

cdf P(a)=

A

integral from -infinity to a of p(x)dx = prob(x<a)

22
Q

the nth moment of a pdf is defined as (discrete case)

A

sum from x=a to x= of x^np(x)delta x

23
Q

nth moment of a pdf for the continuous case

A

integral from a to b of x^np(x)dx

24
Q

1st moment is called the

A

mean or expectation value

25
second moment is called
the mean square
26
the variance for the discrete case is defined as
sum between a and b of p(x)(x-)^2delta x
27
the variance for the continuous case
integral between a and b of p(x)(x-)^2dx
28
the variance is often written as
σ^2
29
σ=sqrt(σ^2) is called
the standard deviation
30
in general, var[x]=
-^2
31
the median divides the CDF into
two equal halves
32
prob(x
prob(x>xmed)=0.5
33
the mode is the values of x for which
the pdf is a maximum
34
for a normal pdf, mean=
median=mode=μ
35
Poisson mean and variance
mean = μ variance = μ
36
uniform mean and variance
mean = 1/2(a+b) variance = 1/12(b-a)^2
37
normal mean and variance
mean = μ variance =σ^2
38
probability =
long run relative frequency of an event given infinite many experimental trials
39
{xi,...,xm} =
random sample from pdf p(x) with mean μ and variance σ^2
40
σ^2 and μ are
fixed but unknown parameters
41
sample mean
μ hat = 1/M Σ from i=1 to M of xi
42
E(μ hat) = μ when
taking all samples in distribution
43
as sample size increases, sample mean
increasingly concentrated near to true mean
44
the central limit theorem
for any pdf with finite variance, as M approaches infinity, u hat follows a normal pdf with mean u and variance σ^2/M
45
the central limit theorem explains importance of normal pdf in statistics but still based on
asymptotic behavior of an infinite ensemble of samples that we didn't actually observe
46
variable probability density function example
chi 2
47