Stats: Chapter 13

What are confidence limits?

The values that state the boundaries of the confidence interval

T or F: Confidence interval is an interval that the probability is .95 that the interval contains the population value

true, The probability is referring to the confidence interval not the population mean

T or F: If N>30 and the null hypothesis is normally shaped t-distribution looks like z-distribution

TRUE! (are all of these going to be true? wtf, you cray)

If H1 is directional then x-bar needs to be in the direction that was predicted

TRUe

True or False: The closer that a t-distribution gets to looking like a normal bell-shaped curve, the higher the df are.

TRUE, this indicates a larger sample size and is consistent with prior theories about normal distribution

What is a confidence interval?

A range of values that probably contains the population value

T or F: The T test is more powerful than the Ztest

FALSE the t test is less powerful than the ztest tcrit>zcrit as df increase tcrit approaches zcrit

Who is student?

Gosset

What does the sampling distribution of t do?

It gives all possible different t values for samples of size N The probability of getting each value if sampling is random from the null-hypothesis population

What is the sampling distribution of t?

It is a probability distribution of the t-values that would occur if all possible different samples of a fixed size N were drawn from the null hypothesis population.

What is required to run a z-test?

Mean and SD of Population bc it uses mean of pop. to test Null hypothesis must know the sampling distribution of the mean

T or F: As the size of the real effect increases so does the difference between x-bar-obt and mu

TRUE!

T or F: Like Sampling distribution of the mean, cab be determined theoretically or empirically

TRUE!

T or F: Most research does not meet the criteria for a z-test

TRUE!

What are degrees of freedom?

The number of scores that are free to vary in calculating a statistic

T or F: By estimating the standard deviation of the pop. using size of sample influences accuracy of the estimate

True

True or false: The wider a confidence interval the greater the confidence that the limits contain the mean.

True (alpha=.05 -> confidence interval contains 95% of scores)

True or False? T-dist. varies uniquely with the degrees of freedom associated with t instead of just the sample size

True! The df of single group t-test is N-1 if there are multiple groups it is N-K

T or F: Studen'ts t and the z-test are very similar.

True.

Why can't we use a z test in most research?

We can guess the mean but we cannot guess the standard deviation. The Z-test requires a large sample, but that's not always available to us.

When is the z-test used?

When the parameters of the Null Hypothesis Population are known (mean and standard deviation)

When do we use the t-test?

When the population standard deviation is unknown

How many t-distributions are there?

one for every df

if Tobtained > T crit then...

reject Null hypothesis