L7 & 8 Statistics Flashcards
(20 cards)
What is a statistical hypothesis test?
A method for determining whether results are due to chance or represent a real effect by comparing to a probability distribution.
What is a probability distribution?
A mathematical description of the probabilities of all possible outcomes of an experiment.
What is the 68-95-99 rule?
68% of data fall within 1 SD, 95% within 2 SD, 99.7% within 3 SD of the mean in a normal distribution.
What is the null hypothesis (H0)?
The assumption that observed results are due to chance and there is no real effect.
What happens if the result is very unlikely under H0?
We reject the null hypothesis and infer a real effect.
Why use a t-distribution instead of a z-distribution?
Because population standard deviation is unknown, and t-distribution adjusts for sample size.
How does the t-distribution change with degrees of freedom?
It is broader with fewer degrees of freedom and approaches a normal distribution with more.
What are the three experimental designs?
One-sample, Between-subjects (independent-measures), and Within-subjects (repeated-measures).
What is a one-sample design?
Compares a group mean to a specific value.
What is an independent-measures design?
Compares means of two separate groups with different participants.
What is a repeated-measures design?
Compares the same group’s performance under two conditions.
What are Type I and Type II errors?
- Type I error: rejecting the null hypothesis of no effect when it is actually true.
- Type II error: not rejecting the null hypothesis of no effect when it is actually false.
Example: Type I and II errors - Type I error: you conclude that spending 10 minutes in nature daily reduces stress when it actually doesn’t.
- Type II error: you conclude that spending 10 minutes in nature daily doesn’t affect stress when it actually does.
What is statistical power?
The probability of correctly rejecting a false null hypothesis (avoiding Type II error).
When to use one-tailed vs two-tailed tests?
One-tailed for directional hypotheses, two-tailed for non-directional.
What is the goal of an independent-measures t-test?
To determine if the difference between two group means is significant.
What is pooled variance?
The average of two sample variances used to estimate standard error in independent-measures t-tests.
Why is pooled variance used?
To combine variance estimates when group sizes are equal (or adjust for unequal sizes).
What is a paired-samples t-test?
Used to compare means from the same group under two conditions.
What are assumptions of t-tests?
- Independent observations 2. Normal populations 3. Equal variances for independent-measures t-test.
What is Cohen’s d?
A measure of effect size indicating the standardized difference between two means.
