Stats Exam 3 Flashcards
Where does a density curve lie on a graph
the x axis
What is the total area under a curve?
1
What is a continuous probability distribution?
a density curve
How do you find the probability association with a normal distribution
- z = x - µ / σ
- then use the Table II
What is a percentile?
Solve for X “unstandardize”
x= µ + zσ
Define statistic
the value of a statistic will vary from one random sample to the next
If the x variable follow a normal distribution with µ and σ, then which rule applies?
68 - 95 - 99.7 %
Parameter
the value of a parameter remains constant
Define Sampling Error
- Because statistics are random variables
- a slight error associated with the estimate
- x - u
What is a sampling distribution
- a probability distribution for all possible samples
If the sample is from a normal poulation then what does x bar have?
a normal sampling distribution
What is σx?
= σ / square rt of n
How are probabilities found?
standardizing using the standard normal table
How are percentiles found?
by unstandardizing from the standard normal table
Define the Central Limit Theorem
- when the sample size n is large is a normal distribution
Define a point estimate?
- single number estimate
- give no indication of the size of the sampling error
Will the point estimate equal the true value?
No, because of sampling error
What does the margine of error indicate
how big the sampling error might be
What is a confidence interval?
a range of estimate for the true population parameter.
= Point Estimate +/- Margin of Error
What does level of confidence mean?
how certain we can be that the true value is contained in the interval (%)
What also increases as the level of confidence increases?
the width of the confidence interval
What happens to the width of the confidence interval when n increases?
the width decreases
If you are given the endpoints of a confidenct interval, how do you calculate the mean?
add and divide by 2
What weight sparates the value of the heaviest 10% al all books from the 90% (90th percentile) what type of question is this?
unstandardizing- look for Z in table II
If you are given *n * in a problem with mean and standard deviation, what is the first thing you need to do?
- convert σ to σx
- use z equation
- look up in table II
which equation do you use to obtain the confidence interval?
t-interval ch 8
