PS211 - Exam 2 - Making Decisions About a Sample Mean

inferential statistics

uses data collected from a small group (a sample) to make predictions, test hypotheses, and draw conclusions about a much larger group (a population)

sampling error

natural statistical difference between a sample's calculated result and the true value of the entire population

• bigger samples → more precise estimates

criterion/alpha

pre-set probability threshold that determines how much evidence you need to reject a null hypothesis

• limit risk of making type I error

most common alpha level

.05

region of rejection

the set of values for a test statistic that leads to the rejection of the null hypothesis

what happens to sample means that fall within region of rejection

reject the null

• there is a difference between sample and population

experimental hypotheses

predict real-world relationships or effects between variables

statistical hypothesis

translate experimental hypotheses into mathematical statements about population parameters

• can be tested with data

  • means, proportions, or correlations

how do we test the null hypotheses and not the alt hypothesis

• assume null is true

• set criteria

• collect data

• accept/reject null

one tailed test

• directional

  • predicts direction of relationship

two tailed test

• nondirectional

  • predicts relationship exists w/o stating which way it will go