This document provides an overview of key concepts in statistics and probability, including:
- Population and sample definitions, types of sampling methods, and observational vs experimental studies.
- Descriptive statistics such as mean, median, variance, standard deviation, and how these are affected by outliers and transformations.
- Probability rules and concepts like independent and dependent events, conditional probability, and multiplication rules.
- Common probability distributions like binomial, normal, and how to calculate expectations and variances.
- Hypothesis testing methods like confidence intervals, test statistics, and p-values.
- Simple linear regression modeling to predict relationships between variables.
Descriptive Statistics Formula Sheet Sample Populatio.docxsimonithomas47935
Descriptive Statistics Formula Sheet
Sample Population
Characteristic statistic Parameter
raw scores x, y, . . . . . X, Y, . . . . .
mean (central tendency) M =
∑ x
n
μ =
∑ X
N
range (interval/ratio data) highest minus lowest value highest minus lowest value
deviation (distance from mean) Deviation = (x − M ) Deviation = (X − μ )
average deviation (average
distance from mean)
∑(x − M )
n
= 0
∑(X − μ )
N
sum of the squares (SS)
(computational formula) SS = ∑ x
2 −
(∑ x)2
n
SS = ∑ X2 −
(∑ X)2
N
variance ( average deviation2 or
standard deviation
2
)
(computational formula)
s2 =
∑ x2 −
(∑ x)2
n
n − 1
=
SS
df
σ2 =
∑ X2 −
(∑ X)2
N
N
standard deviation (average
deviation or distance from mean)
(computational formula) s =
√∑ x
2 −
(∑ x)2
n
n − 1
σ =
√∑ X
2 −
(∑ X)2
N
N
Z scores (standard scores)
mean = 0
standard deviation = ± 1.0
Z =
x − M
s
=
deviation
stand. dev.
X = M + Zs
Z =
X − μ
σ
X = μ + Zσ
Area Under the Normal Curve -1s to +1s = 68.3%
-2s to +2s = 95.4%
-3s to +3s = 99.7%
Using Z Score Table for Normal Distribution
(Note: see graph and table in A-23)
for percentiles (proportion or %) below X
for positive Z scores – use body column
for negative Z scores – use tail column
for proportions or percentage above X
for positive Z scores – use tail column
for negative Z scores – use body column
to discover percentage / proportion between two X values
1. Convert each X to Z score
2. Find appropriate area (body or tail) for each Z score
3. Subtract or add areas as appropriate
4. Change area to % (area × 100 = %)
Regression lines
(central tendency line for all
points; used for predictions
only) formula uses raw
scores
b = slope
a = y-intercept
y = bx + a
(plug in x
to predict y)
b =
∑ xy −
(∑ x)(∑ y)
n
∑ x2 −
(∑ x)2
n
a = My - bMx
where My is mean of y
and Mx is mean of x
SEest (measures accuracy of predictions; same properties as standard deviation)
Pearson Correlation Coefficient
(used to measure relationship;
uses Z scores)
r =
∑ xy−
(∑ x)(∑ y)
n
√(∑ x2−
(∑ x)2
n
)(∑ y2−
(∑ y)2
n
)
r =
degree x & 𝑦 𝑣𝑎𝑟𝑦 𝑡𝑜𝑔𝑒𝑡ℎ𝑒𝑟
degree x & 𝑦 𝑣𝑎𝑟𝑦 𝑠𝑒𝑝𝑎𝑟𝑎𝑡𝑒𝑙𝑦
r
2
= estimate or % of accuracy of predictions
PSYC 2317 Mark W. Tengler, M.S.
Assignment #9
Hypothesis Testing
9.1 Briefly explain in your own words the advantage of using an alpha level (α) = .01
versus an α = .05. In general, what is the disadvantage of using a smaller alpha
level?
9.2 Discuss in your own words the errors that can be made in hypothesis testing.
a. What is a type I error? Why might it occur?
b. What is a type II error? How does it happen?
9.3 The term error is used in two different ways in the context of a hypothesis test.
First, there is the concept of sta
Probability
Random variables and Probability Distributions
The Normal Probability Distributions and Related Distributions
Sampling Distributions for Samples from a Normal Population
Classical Statistical Inferences
Properties of Estimators
Testing of Hypotheses
Relationship between Confidence Interval Procedures and Tests of Hypotheses.
When modeling a system, encountering missing data is common.
What shall a modeler do in the case of unknown or missing information?
When dealing with missing data, it is critical to make correct assumptions to ensure that the system is accurate.
One must common strategy for handling such situations is calculate the average of available data for the similar existing systems (i.e., creating sampling data).
Use this average as a reasonable estimate for the missing value.
Basic statistics for algorithmic tradingQuantInsti
In this presentation we try to understand the core basics of statistics and its application in algorithmic trading.
We start by defining what statistics is. Collecting data is the root of statistics. We need data to analyse and take quantitative decisions.
While analyzing, there are certain parameters for statistics, this branches statistics into two - descriptive statistics & inferential statistics.
This data that we have collected can be classified into uni-variate and bi-variate. It also tries to explain the fundamental difference.
Going Further we also cover topics like regression line, Coefficient of Determination, Homoscedasticity and Heteroscedasticity.
In this way the presentation look at various aspects of statistics which are used for algorithmic trading.
To learn the advanced applications of statistics for HFT & Quantitative Trading connect with us one our website: www.quantinsti.com.
We develop a new method to optimize portfolios of options in a market where European calls and puts are available with many exercise prices for each of several potentially correlated underlying assets. We identify the combination of asset-specific option payoffs that maximizes the Sharpe ratio of the overall portfolio: such payoffs are the unique solution to a system of integral equations, which reduce to a linear matrix equation under suitable representations of the underlying probabilities. Even when implied volatilities are all higher than historical volatilities, it can be optimal to sell options on some assets while buying options on others, as hedging demand outweighs demand for asset-specific returns.
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Editable Toolkit to help you reuse our content: 700 Powerpoint slides | 35 Excel sheets | 84 minutes of Video training
This PowerPoint presentation is only a small preview of our Toolkits. For more details, visit www.domontconsulting.com
Descriptive Statistics Formula Sheet Sample Populatio.docxsimonithomas47935
Descriptive Statistics Formula Sheet
Sample Population
Characteristic statistic Parameter
raw scores x, y, . . . . . X, Y, . . . . .
mean (central tendency) M =
∑ x
n
μ =
∑ X
N
range (interval/ratio data) highest minus lowest value highest minus lowest value
deviation (distance from mean) Deviation = (x − M ) Deviation = (X − μ )
average deviation (average
distance from mean)
∑(x − M )
n
= 0
∑(X − μ )
N
sum of the squares (SS)
(computational formula) SS = ∑ x
2 −
(∑ x)2
n
SS = ∑ X2 −
(∑ X)2
N
variance ( average deviation2 or
standard deviation
2
)
(computational formula)
s2 =
∑ x2 −
(∑ x)2
n
n − 1
=
SS
df
σ2 =
∑ X2 −
(∑ X)2
N
N
standard deviation (average
deviation or distance from mean)
(computational formula) s =
√∑ x
2 −
(∑ x)2
n
n − 1
σ =
√∑ X
2 −
(∑ X)2
N
N
Z scores (standard scores)
mean = 0
standard deviation = ± 1.0
Z =
x − M
s
=
deviation
stand. dev.
X = M + Zs
Z =
X − μ
σ
X = μ + Zσ
Area Under the Normal Curve -1s to +1s = 68.3%
-2s to +2s = 95.4%
-3s to +3s = 99.7%
Using Z Score Table for Normal Distribution
(Note: see graph and table in A-23)
for percentiles (proportion or %) below X
for positive Z scores – use body column
for negative Z scores – use tail column
for proportions or percentage above X
for positive Z scores – use tail column
for negative Z scores – use body column
to discover percentage / proportion between two X values
1. Convert each X to Z score
2. Find appropriate area (body or tail) for each Z score
3. Subtract or add areas as appropriate
4. Change area to % (area × 100 = %)
Regression lines
(central tendency line for all
points; used for predictions
only) formula uses raw
scores
b = slope
a = y-intercept
y = bx + a
(plug in x
to predict y)
b =
∑ xy −
(∑ x)(∑ y)
n
∑ x2 −
(∑ x)2
n
a = My - bMx
where My is mean of y
and Mx is mean of x
SEest (measures accuracy of predictions; same properties as standard deviation)
Pearson Correlation Coefficient
(used to measure relationship;
uses Z scores)
r =
∑ xy−
(∑ x)(∑ y)
n
√(∑ x2−
(∑ x)2
n
)(∑ y2−
(∑ y)2
n
)
r =
degree x & 𝑦 𝑣𝑎𝑟𝑦 𝑡𝑜𝑔𝑒𝑡ℎ𝑒𝑟
degree x & 𝑦 𝑣𝑎𝑟𝑦 𝑠𝑒𝑝𝑎𝑟𝑎𝑡𝑒𝑙𝑦
r
2
= estimate or % of accuracy of predictions
PSYC 2317 Mark W. Tengler, M.S.
Assignment #9
Hypothesis Testing
9.1 Briefly explain in your own words the advantage of using an alpha level (α) = .01
versus an α = .05. In general, what is the disadvantage of using a smaller alpha
level?
9.2 Discuss in your own words the errors that can be made in hypothesis testing.
a. What is a type I error? Why might it occur?
b. What is a type II error? How does it happen?
9.3 The term error is used in two different ways in the context of a hypothesis test.
First, there is the concept of sta
Probability
Random variables and Probability Distributions
The Normal Probability Distributions and Related Distributions
Sampling Distributions for Samples from a Normal Population
Classical Statistical Inferences
Properties of Estimators
Testing of Hypotheses
Relationship between Confidence Interval Procedures and Tests of Hypotheses.
When modeling a system, encountering missing data is common.
What shall a modeler do in the case of unknown or missing information?
When dealing with missing data, it is critical to make correct assumptions to ensure that the system is accurate.
One must common strategy for handling such situations is calculate the average of available data for the similar existing systems (i.e., creating sampling data).
Use this average as a reasonable estimate for the missing value.
Basic statistics for algorithmic tradingQuantInsti
In this presentation we try to understand the core basics of statistics and its application in algorithmic trading.
We start by defining what statistics is. Collecting data is the root of statistics. We need data to analyse and take quantitative decisions.
While analyzing, there are certain parameters for statistics, this branches statistics into two - descriptive statistics & inferential statistics.
This data that we have collected can be classified into uni-variate and bi-variate. It also tries to explain the fundamental difference.
Going Further we also cover topics like regression line, Coefficient of Determination, Homoscedasticity and Heteroscedasticity.
In this way the presentation look at various aspects of statistics which are used for algorithmic trading.
To learn the advanced applications of statistics for HFT & Quantitative Trading connect with us one our website: www.quantinsti.com.
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This Digital Transformation and IT Strategy Toolkit was created by ex-McKinsey, Deloitte and BCG Management Consultants, after more than 5,000 hours of work. It is considered the world's best & most comprehensive Digital Transformation and IT Strategy Toolkit. It includes all the Frameworks, Best Practices & Templates required to successfully undertake the Digital Transformation of your organization and define a robust IT Strategy.
Editable Toolkit to help you reuse our content: 700 Powerpoint slides | 35 Excel sheets | 84 minutes of Video training
This PowerPoint presentation is only a small preview of our Toolkits. For more details, visit www.domontconsulting.com
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Statistics_Cheat_sheet_1567847508.pdf
1. Population entire collection of objects or
individuals about which information is desired.
➔ easier to take a sample
◆ Sample part of the population
that is selected for analysis
◆ Watch out for:
● Limited sample size that
might not be
representative of
population
◆ Simple Random Sampling
Every possible sample of a certain
size has the same chance of being
selected
Observational Study there can always be
lurking variables affecting results
➔ i.e, strong positive association between
shoe size and intelligence for boys
➔ **should never show causation
Experimental Study lurking variables can be
controlled; can give good evidence for causation
Descriptive Statistics Part I
➔ Summary Measures
➔ Mean arithmetic average of data
values
◆ **Highly susceptible to
extreme values (outliers).
Goes towards extreme values
◆ Mean could never be larger or
smaller than max/min value but
could be the max/min value
➔ Median in an ordered array, the
median is the middle number
◆ **Not affected by extreme
values
➔ Quartiles split the ranked data into 4
equal groups
◆ Box and Whisker Plot
➔ Range = Xmaximum Xminimum
◆ Disadvantages: Ignores the
way in which data are
distributed; sensitive to outliers
➔ Interquartile Range (IQR) = 3rd
quartile 1st quartile
◆ Not used that much
◆ Not affected by outliers
➔ Variance the average distance
squared
sx
2 = n 1
(x x)
∑
n
i=1
i
2
◆ gets rid of the negative
sx
2
values
◆ units are squared
➔ Standard Deviation shows variation
about the mean
s =
√ n 1
(x x)
∑
n
i=1
i
2
◆ highly affected by outliers
◆ has same units as original
data
◆ finance = horrible measure of
risk (trampoline example)
Descriptive Statistics Part II
Linear Transformations
➔ Linear transformations change the
center and spread of data
➔ ar(a X) V ar(X)
V + b = b2
➔ Average(a+bX) = a+b[Average(X)]
2. ➔ Effects of Linear Transformations:
◆ a + b*mean
meannew =
◆ a + b*median
mediannew =
◆ *stdev
stdevnew = b
| |
◆ *IQR
IQRnew = b
| |
➔ Zscore new data set will have mean
0 and variance 1
z = S
X X
Empirical Rule
➔ Only for moundshaped data
Approx. 95% of data is in the interval:
x s , x s ) s
( 2 x + 2 x = x + / 2 x
➔ only use if you just have mean and std.
dev.
Chebyshev's Rule
➔ Use for any set of data and for any
number k, greater than 1 (1.2, 1.3, etc.)
➔ 1 1
k2
➔ (Ex) for k=2 (2 standard deviations),
75% of data falls within 2 standard
deviations
Detecting Outliers
➔ Classic Outlier Detection
◆ doesn't always work
◆ z
| | = |
| S
X X |
| ≥ 2
➔ The Boxplot Rule
◆ Value X is an outlier if:
X<Q11.5(Q3Q1)
or
X>Q3+1.5(Q3Q1)
Skewness
➔ measures the degree of asymmetry
exhibited by data
◆ negative values= skewed left
◆ positive values= skewed right
◆ if = don't need
.8
skewness
| | < 0
to transform data
Measurements of Association
➔ Covariance
◆ Covariance > 0 = larger x,
larger y
◆ Covariance < 0 = larger x,
smaller y
◆ s (x )(y )
xy = 1
n 1 ∑
n
i=1
x y
◆ Units = Units of x Units of y
◆ Covariance is only +, , or 0
(can be any number)
➔ Correlation measures strength of a
linear relationship between two
variables
◆ rxy =
covariancexy
(std.dev. )(std. dev. )
x y
◆ correlation is between 1 and 1
◆ Sign: direction of relationship
◆ Absolute value: strength of
relationship (0.6 is stronger
relationship than +0.4)
◆ Correlation doesn't imply
causation
◆ The correlation of a variable
with itself is one
Combining Data Sets
➔ Mean (Z) = X Y
Z = a + b
➔ Var (Z) = V ar(X) V ar(Y )
sz
2 = a2 + b2
+
abCov(X, )
2 Y
Portfolios
➔ Return on a portfolio:
R R
Rp = wA A + wB B
◆ weights add up to 1
◆ return = mean
◆ risk = std. deviation
➔ Variance of return of portfolio
s s
s2
p = w2
A
2
A + w2
B
2
B + w w (s )
2 A B A,B
◆ Risk(variance) is reduced when
stocks are negatively
correlated. (when there's a
negative covariance)
Probability
➔ measure of uncertainty
➔ all outcomes have to be exhaustive
(all options possible) and mutually
exhaustive (no 2 outcomes can
occur at the same time)
3. Probability Rules
1. Probabilities range from
rob(A)
0 ≤ P ≤ 1
2. The probabilities of all outcomes must
add up to 1
3. The complement rule = A happens
or A doesn't happen
(A) (A)
P = 1 P
(A) (A)
P + P = 1
4. Addition Rule:
(A or B) (A) (B) (A and B)
P = P + P P
Contingency/Joint Table
➔ To go from contingency to joint table,
divide by total # of counts
➔ everything inside table adds up to 1
Conditional Probability
➔ (A|B)
P
➔ (A|B)
P = P(B)
P(A and B)
➔ Given event B has happened, what is
the probability event A will happen?
➔ Look out for: "given", "if"
Independence
➔ Independent if:
or
(A|B) (A)
P = P (B|A) (B)
P = P
➔ If probabilities change, then A and B
are dependent
➔ **hard to prove independence, need
to check every value
Multiplication Rules
➔ If A and B are INDEPENDENT:
(A and B) (A) (B)
P = P P
➔ Another way to find joint probability:
(A and B) (A|B) (B)
P = P P
(A and B) (B|A) (A)
P = P P
2 x 2 Table
Decision Analysis
➔ Maximax solution = optimistic
approach. Always think the best is
going to happen
➔ Maximin solution = pessimistic
approach.
➔ Expected Value Solution =
MV (P ) (P )... (P )
E = X1 1 + X2 2 + Xn n
Decision Tree Analysis
➔ square = your choice
➔ circle = uncertain events
Discrete Random Variables
➔ (x) (X )
PX = P = x
Expectation
➔ = E(x) =
μx P(X )
∑xi = xi
➔ Example: 2)(0.1) 3)(0.5) .7
( + ( = 1
Variance
➔ (x )
σ2
= E 2
μx
2
➔ Example:
2) (0.1) 3) (0.5) 1.7) .01
( 2
+ ( 2
( 2
= 2
Rules for Expectation and Variance
➔ (s) a bμ
μs = E = + x
➔ Var(s)= b2
σ2
Jointly Distributed Discrete Random
Variables
➔ Independent if:
(X and Y ) (x) (y)
Px,y = x = y = Px Py
4. ➔ Combining Random Variables
◆ If X and Y are independent:
(X ) (X) (Y )
E + Y = E + E
ar(X ) ar(X) ar(Y )
V + Y = V + V
◆ If X and Y are dependent:
(X ) (X) (Y )
E + Y = E + E
ar(X ) ar(X) ar(Y ) Cov(X, )
V + Y = V + V + 2 Y
➔ Covariance:
ov(X, ) (XY ) (X)E(Y )
C Y = E E
➔ If X and Y are independent, Cov(X,Y)
= 0
Binomial Distribution
➔ doing something n times
➔ only 2 outcomes: success or failure
➔ trials are independent of each other
➔ probability remains constant
1.) All Failures
(all failures) 1 )
P = ( p n
2.) All Successes
(all successes)
P = pn
3.) At least one success
(at least 1 success) 1 )
P = 1 ( p n
4.) At least one failure
P(at least 1 failure) = 1 pn
5.) Binomial Distribution Formula for
x=exact value
6.) Mean (Expectation)
(x) p
μ = E = n
7.) Variance and Standard Dev.
pq
σ2
= n
σ = √npq
q = 1 p
Binomial Example
Continuous Probability Distributions
➔ the probability that a continuous
random variable X will assume any
particular value is 0
➔ Density Curves
◆ Area under the curve is the
probability that any range of
values will occur.
◆ Total area = 1
Uniform Distribution
◆ nif (a, )
X ~ U b
Uniform Example
(Example cont'd next page)
5. ➔ Mean for uniform distribution:
(X)
E = 2
(a+b)
➔ Variance for unif. distribution:
ar(X)
V = 12
(b a)2
Normal Distribution
➔ governed by 2 parameters:
(the mean) and (the standard
μ σ
deviation)
➔ (μ, )
X ~ N σ2
Standardize Normal Distribution:
Z = σ
X μ
➔ Zscore is the number of standard
deviations the related X is from its
mean
➔ **Z< some value, will just be the
probability found on table
➔ **Z> some value, will be
(1probability) found on table
Normal Distribution Example
Sums of Normals
Sums of Normals Example:
➔ Cov(X,Y) = 0 b/c they're independent
Central Limit Theorem
➔ as n increases,
➔ should get closer to (population
x μ
mean)
➔ mean( )
x = μ
➔ variance x) n
( = σ2
/
➔ (μ, )
X ~ N n
σ2
◆ if population is normally distributed,
n can be any value
◆ any population, n needs to be 0
≥ 3
➔ Z =
X μ
σ/√n
Confidence Intervals = tells us how good our
estimate is
**Want high confidence, narrow interval
**As confidence increases , interval also
increases
A. One Sample Proportion
➔ p
︿
= x
n = sample size
number of successes in sample
➔
➔ We are thus 95% confident that the true
population proportion is in the interval…
➔ We are assuming that n is large, n >5 and
p
︿
our sample size is less than 10% of the
population size.
6. Standard Error and Margin of Error
Example of Sample Proportion Problem
Determining Sample Size
n = e2
(1.96) p(1 p)
2︿ ︿
➔ If given a confidence interval, is
p
︿
the middle number of the interval
➔ No confidence interval; use worst
case scenario
◆ =0.5
p
︿
B. One Sample Mean
For samples n > 30
Confidence Interval:
➔ If n > 30, we can substitute s for
so that we get:
σ
For samples n < 30
T Distribution used when:
➔ is not known, n < 30, and data is
σ
normally distributed
*Stata always uses the tdistribution when
computing confidence intervals
Hypothesis Testing
➔ Null Hypothesis:
➔ , a statement of no change and is
H0
assumed true until evidence indicates
otherwise.
➔ Alternative Hypothesis: is a
Ha
statement that we are trying to find
evidence to support.
➔ Type I error: reject the null hypothesis
when the null hypothesis is true.
(considered the worst error)
➔ Type II error: do not reject the null
hypothesis when the alternative
hypothesis is true.
Example of Type I and Type II errors
Methods of Hypothesis Testing
1. Confidence Intervals **
2. Test statistic
3. Pvalues **
➔ C.I and Pvalues always safe to do
because don’t need to worry about
size of n (can be bigger or smaller
than 30)
7. One Sample Hypothesis Tests
1. Confidence Interval (can be
used only for twosided tests)
2. Test Statistic Approach
(Population Mean) 3. Test Statistic Approach (Population
Proportion)
4. PValues
➔ a number between 0 and 1
➔ the larger the pvalue, the more
consistent the data is with the null
➔ the smaller the pvalue, the more
consistent the data is with the
alternative
➔ **If P is low (less than 0.05),
must go reject the null
H0
hypothesis
8. Two Sample Hypothesis Tests
1. Comparing Two Proportions
(Independent Groups)
➔ Calculate Confidence Interval
➔ Test Statistic for Two Proportions 2. Comparing Two Means (large
independent samples n>30)
➔ Calculating Confidence Interval
➔ Test Statistic for Two Means
Matched Pairs
➔ Two samples are DEPENDENT
Example:
9. Simple Linear Regression
➔ used to predict the value of one
variable (dependent variable) on the
basis of other variables (independent
variables)
➔ X
Y
︿
= b0 + b1
➔ Residual: e = Y Y
︿
fitted
➔ Fitting error:
X
ei = Y i Y i
︿
= Y i b0 bi i
◆ e is the part of Y not related
to X
➔ Values of and which minimize
b0 b1
the residual sum of squares are:
(slope) b1 = rsx
sy
X
b0 = Y b1
➔ Interpretation of slope for each
additional x value (e.x. mile on
odometer), the y value decreases/
increases by an average of value
b1
➔ Interpretation of yintercept plug in
0 for x and the value you get for is
y
︿
the yintercept (e.x.
y=3.250.0614xSkippedClass, a
student who skips no classes has a
gpa of 3.25.)
➔ **danger of extrapolation if an x
value is outside of our data set, we
can't confidently predict the fitted y
value
Properties of the Residuals and Fitted
Values
1. Mean of the residuals = 0; Sum of
the residuals = 0
2. Mean of original values is the same
as mean of fitted values Y = Y
︿
3.
4. Correlation Matrix
➔ corr Y , )
(
︿
e = 0
A Measure of Fit: R2
➔ Good fit: if SSR is big, SEE is small
➔ SST=SSR, perfect fit
➔ : coefficient of determination
R2
R2
= SSR
SST = 1 SST
SSE
➔ is between 0 and 1, the closer
R2
R2
is to 1, the better the fit
➔ Interpretation of : (e.x. 65% of the
R2
variation in the selling price is explained by
the variation in odometer reading. The rest
35% remains unexplained by this model)
➔ ** doesn’t indicate whether model
R2
is adequate**
➔ As you add more X’s to model, R2
goes up
➔ Guide to finding SSR, SSE, SST
10. Assumptions of Simple Linear Regression
1. We model the AVERAGE of something
rather than something itself
2.
◆ As (noise) gets bigger, it’s
ε
harder to find the line
Estimating Se
➔ S2
e = n 2
SSE
➔ is our estimate of σ
Se
2 2
➔ is our estimate of σ
Se = √Se
2
➔ 95% of the Y values should lie within
the interval X 1.96S
b0 + b1
+
e
Example of Prediction Intervals:
Standard Errors for and b
b1 0
➔ standard errors when noise
➔ amount of uncertainty in our
sb0
estimate of (small s good, large s
β0
bad)
➔ amount of uncertainty in our
sb1
estimate of β1
Confidence Intervals for and b
b1 0
➔
➔
➔
➔
➔ n small → bad
big → bad
se
small→ bad (wants x’s spread out for
s2
x
better guess)
Regression Hypothesis Testing
*always a twosided test
➔ want to test whether slope ( ) is
β1
needed in our model
➔ : = 0 (don’t need x)
H0 β1
: 0 (need x)
Ha =
β1 /
➔ Need X in the model if:
a. 0 isn’t in the confidence
interval
b. t > 1.96
c. Pvalue < 0.05
Test Statistic for Slope/Yintercept
➔ can only be used if n>30
➔ if n < 30, use pvalues
11. Multiple Regression
➔
➔ Variable Importance:
◆ higher tvalue, lower pvalue =
variable is more important
◆ lower tvalue, higher pvalue =
variable is less important (or not
needed)
Adjusted Rsquared
➔ k = # of X’s
➔ Adj. Rsquared will as you add junk x
variables
➔ Adj. Rsquared will only if the x you
add in is very useful
➔ **want Adj. Rsquared to go up and Se
low for better model
The Overall F Test
➔ Always want to reject F test (reject
null hypothesis)
➔ Look at pvalue (if < 0.05, reject null)
➔ : (don’t
H0 ...
β1 = β2 = β3 = βk = 0
need any X’s)
: (need at
Ha ... =
β1 = β2 = β3 = βk / 0
least 1 X)
➔ If no x variables needed, then SSR=0
and SST=SSE
Modeling Regression
Backward Stepwise Regression
1. Start will all variables in the model
2. at each step, delete the least important
variable based on largest pvalue above
0.05
3. stop when you can’t delete anymore
➔ Will see Adj. Rsquared and Se
Dummy Variables
➔ An indicator variable that takes on a
value of 0 or 1, allow intercepts to
change
Interaction Terms
➔ allow the slopes to change
➔ interaction between 2 or more x
variables that will affect the Y variable
How to Create Dummy Variables (Nominal
Variables)
➔ If C is the number of categories, create
(C1) dummy variables for describing
the variable
➔ One category is always the
“baseline”, which is included in the
intercept
Recoding Dummy Variables
Example: How many hockey sticks sold in
the summer (original equation)
ockey 00 0Wtr 0Spr 0Fall
h = 1 + 1 2 + 3
Write equation for how many hockey sticks
sold in the winter
ockey 10 0Fall 0Spri 0Summer
h = 1 + 2 3 1
➔ **always need to get same exact
values from the original equation
12. Regression Diagnostics
Standardize Residuals
Check Model Assumptions
➔ Plot residuals versus Yhat
➔ Outliers
◆ Regression likes to move
towards outliers (shows up
as being really high)
R2
◆ want to remove outlier that is
extreme in both x and y
➔ Nonlinearity (ovtest)
◆ Plotting residuals vs. fitted
values will show a
relationship if data is
nonlinear ( also high)
R2
◆ Log transformation
accommodates nonlinearity,
reduces right skewness in the Y,
eliminates heteroskedasticity
◆ **Only take log of X variable
so that we can compare models.
Can’t compare models if you take log
of Y.
◆ Transformations cheatsheet
◆ ovtest: a significant test
statistic indicates that
polynomial terms should be
added
◆ :
H0 ata o transformation
d = n
:
Ha ata = o transformation
d / n
➔ Normality (sktest)
◆ :
H0 ata ormality
d = n
:
Ha ata = ormality
d / n
◆ don’t want to reject the null
hypothesis. Pvalue should
be big
➔ Homoskedasticity (hettest)
◆ :
H0 ata omoskedasticity
d = h
◆ ata = omoskedasticity
Ha : d / h
◆ Homoskedastic: band around the
values
◆ Heteroskedastic: as x goes up,
the noise goes up (no more band,
fanshaped)
◆ If heteroskedastic, fix it by
logging the Y variable
◆ If heteroskedastic, fix it by
making standard errors robust
➔ Multicollinearity
◆ when x variables are highly
correlated with each other.
◆ > 0.9
R2
◆ pairwise correlation > 0.9
◆ correlate all x variables, include
y variable, drop the x variable
that is less correlated to y
Summary of Regression Output