UNIT 3 and UNIT 4 COMBO Flashcards
when does a trial of a simulation end?
Generally there are two cases:
- You want to know the probability of having x successes in n attempts (getting 3 smokers in a group of 5 students). Trials end when you get to n (get to 5 students). You record the number of smokers for each trial.
- You want to know how many attempts it takes to get f successes. Trials end when you get f successes. Record the number of attempts.
What type of probability when you are looking for at least one success in twelve attempts?
1 - p(NONE)
or “not zero”
1-binopdf(12, p, 0)
What is prospective study?
Prosepctive study is when you study the experimental unit’s present and futrue response variable.
RAND VARIABLE:
X has mean y and standard deviation of z.
A has mean b and standard deviation c.
Find: Mean, SD and VAR of: 5A
mean: 5b
sd: 5c
var: 25c2
what’s the difference between response bias and nonresponse bias?
response bias is anything in a survey design that influences responses falls under the heading of response bias (wording of questions).
Nonresponse bias is bias introduced to a sample when a large fraction of those sampled fails to respond.those who respond are likely to not represent the entire sample.
what is the law of large numbers?
states that in the long run.. (NOT SHORT RUN)
The relative frequency settles down to true probability.
(you’ll have 50% heads after an infinite number of coin flips with a fair coin).
Don’t make short run predictions.. coins don’t owe you “tails”
What are humans bad at ?
Humans are bad at generating random numbers.
What’s the difference between lurking and confounding?
Lurking varibles, on one hand, infer the association between the two varibles;
confounding variables, on the other hand, make it unclear which variable has had an impact on which in an experiment.
How many successes can you expect when you know p? (mean of binormial)
np.
Makes sense, if 30% like butter, out of 50 people you would expect (50)(.3)= 15 to like butter
np is the mean of the binomial distribution
What is the difference between a study and an experiment?
In a study you are basically just watching.
In an experiment you are manipulating factors and (hopefully randomly) assigning treatments.
Sometimes people call an experiment a study.
what is probability?
THE LONG RUN RELATIVE FREQUENCY!!
How are voluntary and convenience samples similar?
With voluntary, people choose them selves,
with covenience, the people are just chosen by researchers without using a random method, neither uses randomness and both are prone to BIAS.
Why blind the treatment givers?
The treatment givers may behave differently as they administer the actual meds vs when they administer the placebo.
What is a control group?
A group in an experiment without the treatment that is compared to groups with treatments to make results or conclusions.
The control group helps us see what would happen anyway. without any treatment so that we can see the true effect of the treatment.
Give examples of when you would block
Looking to see impact of different leather preservers on chairs in an airport. You might block according to proximity to window, or proximity to main entrance. The window seats will get more light and the ones closest to entrance may get more use, they will age and wear differently so you want to make sure some in each group get the different treatments.
OR, pain medicine. You might block by gender as males and females might react differently.
What is the problem with convenient sampling?
The sample may not be representative as it is not randomized to include every type of person.
Friends and family are convenient but they likely share similar opinions and thus the sample is not representative of a population.
Explain two types of experimental design.
- )Randomized Block Design: randomization occurs within the blocks only. MATCHING IS BLOCKING
- ) Completely Randomized Design: all of the experimental units have the same chance at recieving a treatment.
what is independent? What are the two equations to test for independence?
when P(A)=P(A|B) OR P(A)*P(B)=P(A and B)
When the probability of A is the same even when B is also true.
Knowing B does not affect the probability of A.
What do we call it when two things can’t happen at the same time?
disjoint OR mutually exclusive
When to use general MULT and what is it?
AND probability. Use when associated.
P(this)*P(that | this).
P(A)*P(B given A)
IT ALWAYS WORKS FOR ALL SITUATIONS.
When indep, the P(that|this) = P(that). So you end up with the simpler independent version, P(this)*P(that)
What is sample size and how does it compare with the fraction of a population?
Sample size is the number of individuals in a sample. The sample size determines how well the sample represents the population, not a fraction of the population sampled. The fraction of the population that you’ve sampled doesnt matter. Its the sample size its self thats most important.
Can you stratify in an experiment?
NO. stratification is a sampling method, blocking is method used in experiments.
They are sort of similar ideas.
RAND VARIABLE:
X has mean y and standard deviation of z.
A has mean b and standard deviation c.
Find: Mean, SD and VAR of: X + 12
mean: y+12
SD z
var: z2
can independent events be disjoint?
EXPLAIN
NO, if they are independent, then knowing one doesn’t change the probability of the other, but if they are disjoint, knowing one makes the other impossible, so it does change the probability of the other to 0