Quant Flashcards
Describe where the Mean, median and mode sit with positive and negative skew
Positive Skew = large number of low observations
Mode, median, mean
Negative Skew = large number of high observations
Mean, median, mode
the mean always sits in the less sloped tail
What are the different probabilities of standard deviations?
68% µ ± 1 standard deviations.
90% µ ± 1.65 to standard deviations.
95% µ ± 1.96 to standard deviations.
99% µ ± 2.58 to standard deviations.
note this is plus and minus! so SD is 34% on each side!
What are Z, T and Chi-Square and F tests used for
Z - Validate a sample belongs to the same population
T - Compare the mean of two samples (e.g paired comparison test)
Chi Square - Compare categorical values (e.g Goodness of fit test) - single population
F - test the equality of two variances (SD 1 / SD2), df= n-1
In a lin-log model, log refers to which variable?
Lin= Independant
Log = dependent
Explain Type 1 Type 2, significance and power of a test
Type 1: Reject Null when True
Significance: P of Type 1 Error
Type 2: Fail to reject null when it is false
Power of a test: 1- Type 2 error
Define an unbiased, consistent and efficient estimator
Unbiased
An unbiased estimator is one for which the expected value of the estimator is equal to the parameter you are trying to estimate
Consistent
A consistent estimator provides a more accurate estimate of the parameter as the sample size increases.
Efficient
if the variance of its sampling distribution is smaller than all the other unbiased estimators of the parameter you are trying to estimate. The sample mean, for example, is an unbiased and efficient estimator of the population mean.
How do you calculate the harmonic mean
1/ all numbers
add them up
n (number of observations) / Sum
answer
Calculate coefficient of variation
SD / mean
Standardize a random variable and calculate a Z score
mean - observation
/
SD
mean - observation
/
(SD/SQRn)
What is the bayes formula
PA|B =
P(B|A) x P(B) (Joint Probability
/
PB (total probability)
Define the difference between an outcome and an event
An event is defined as a single outcome or a set of outcomes;
an outcome is an observed value of a random variable.
Difference between Jacknife and Bootstrap?
Jackknife: Calculate sample means with one observation removed
Bootstrap: Drawing repeated samples replacing the sampled observations each time, equal to the sample size
Explain the impact of DF and reliability factor on the width of a confidence inverval
DF shrinks as gets larger
RF - widens it
Sample size - narrows it
What is stratified random sampling
In stratified random sampling, one divides the population into subpopulations and randomly samples from within the subpopulations.
How do you compute a t-statistic?
(x1-x2 ) - (u1-u2)
/
(SE1 + se2)^.5
