UNIT 7 Flashcards
parameter
A number that describes some characteristic of the population.
-parameter is usually unknown because it is often impossible to examine the entire population.
Statistic
A number that describes some characteristic of a sample.
computed
directly from the sample data. We often use a statistic to estimate an unknown parameter.
Unbiased estimator
A statistic used to estimate a parameter.
-mean of its sampling distribution is equal to the true value of the parameter being estimated.
population distribution
Gives the values of the variable of interest for all individuals in the population.
distribution os sample data
Gives the values of the variable of interest for the individuals in the sample.
sampling distribution
Gives the values of the statistic for all possible samples of the same size taken from the population.
Variability of a statistic
How much the value of the statistic varies from sample to sample.
what is the variability of a statistic described by? How is it determined?
It is described by the spread of its sampling distribution.
- spread is determined primarily by the size of the random sample.
what is the relationship between variability and size of a sample
the large the sample size, the lower the variability
The Central Limit Theorem (CLT)
If a random sample of n observations is
selected from any population and the sample
size is sufficiently large ( n ≥ 30), then the
sampling distribution of x is approximately
Normal.
Normal Condition for sample means
If the population distribution is Normal,
then so is the sampling distribution of x.
This is true no matter what the sample
size n is.
• If the population distribution is not Normal, the CLT tells us that the sampling distribution of x will be approximately Normal in most cases if n ≥ 30.
