Chapter 9 - t-tests

A researcher failed to reject the null hypothesis with a two-tailed test using α = .05. If the researcher had used the same data with a one-tailed test, what can we conclude?

It is impossible to tell whether or not the researcher would reject the null hypothesis using a one-tailed test.

Why do t distribution to be flatter and more spread out than the normal distribution is?

The denominator of the t statistic contains the sample standard deviation, which is different for different samples. The z-score uses the population standard deviation, which is the same for different samples. Therefore, the t stat has greater variability

Assuming all other factors stay the same, what happens to the proportion of the data in both tails as the degree freedom increases with the t-stats

The proportion in the two tails combined decreases

Explain what is measured by the sample standard deviation

The sample standard deviation describes he variability of the scores in the sample. In this cause distance between a score and the sample mean i

When n is especially small, the t distribution is __________ and ____________.

flatter, more spread out

As sample size increases, the likelihood of rejecting the null hypothesis ____________

increases

What is the major problem with z-score stats?

it requires knowing the population variance, which is often difficult to obtain

A sample is selected from a population and a treatment is administered to the sample. If there is a 3-point difference between the sample mean and the original population mean, which set of sample characteristics has the greatest likelihood of rejecting the null hypothesis?

s2 = 4 for a sample with n = 10

Assumptions for hypothesis testing using the t stat

the population must be normal the values in the sample must be consistent of independent observations the population standard deviation is unknown

The standard error provides a measure of...

the standard distance between a sample mean and the population mean

As the sample variability increases, the likelihood of reject the null hypothesis ________________

decreases

Measure of effect size tend to ____________ as sample variance increases

decreases

Under what circumstances is a t stat used instead of a z-score for a hypothesis test?

When theata is unknown