Single Sample t test, Effect Size, Confidence Intervals Flashcards
What is the difference between z test and t tests?
The equations are the same except for that the t test uses an estimated standard error of the mean (s-x bar) whereas the z test uses a standard error of the mean.
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. It gives (1) all the possible different t values for samples of size N and (2) the probability of getting each value if sampling is random from the null-hypothesis population.
If the null-hypothesis population is normally shaped, or if N 大于等于 30, what does the t distribution look like?
The t distribution looks very much like the z distribution, except that there is a family of t curves that vary with sample size.
What is degrees of freedom?
The degrees of freedom (df) for any statistic is the number of scores that are free to vary in calculating that statistic.
The t distribution varies with the degrees of freedom.
df=N-1
How does the shape of t distribution change in relation to the degrees of freedom?
The higher the degrees of freedom, the closer the t distribution approaches the normal curve. When df = infinity, the t distribution is identical to the z distribution.
Given an alpha level, which one is higher when we compare the critical values of t or the critical values of z?
The critical value of t is higher than for z, making the t test less powerful than the z test.
What is an interval estimation vs a point estimation?
IQ average of profs = 135 is a point estimation
Give a range of values for which one is reasonably confident that the range includes the population mean. (interval estimation)
What is a confidence interval?
A CI is a range of values that probably contains the population value.
The 95% confidence interval is an interval such that the probability is 0.95 that the interval contains the population value.
What are the values that bound the confidence interval called?
Confidence limits
How do you report the CI?
It is not technically proper to state “the probability is 0.95 that the population mean lies within the interval.”
Rather, the proper statement is “the probability is 0.95 that the interval contains the population mean.”
Difference between 95% and 99% CI?
the larger the interval, the more confidence we have
that the interval contains the population mean.
