Differences Across Two Groups Flashcards
What are the two possibilities when we have two samples that are different?
a) The two samples are different because of sampling variability
b) We have two samples where different is beyond sampling variability, so true difference
What are the pooled degrees for standard error, assuming equal standard deviation?
n1 + n2 - 2
Compare the degrees of freedom for assuming equal and unequal standard deviations
Always smaller degrees of freedom under unequal standard deviation, perceived as more conservative
What have we assumed about data when checking differences between two groups?
- Independence of the data WITHIN and BETWEEN the groups
- The data are normally distributed
Why are hypothesis tests distinct from confidence intervals?
C.Interval contains a range of values for the parameter that are consistent with the data given a success rate
A hypothesis test tests one value is the true value
What are the three types of hypothesis?
Research Hypothesis
Null Hypothesis
Alternative Hypothesis
Describe a research hypothesis
Hypothesis that research is designed to investigate
Describe a null hypothesis
Hypothesis that we test and is typically a sceptical reaction to the research hypothesis
Describe an alternative hypothesis
Specifies a departure from H0, typically corresponsd to the research hypothesis
If H0 is true, should the test statistic be small or large?
Small
What do we do to decide if a test statistic is typically under the null hypothesis?
Compare our observed value with a reference distribution
Describe the p value
Probability of observing a test statistic at least as extreme as the one observed, given the null hypothesis is true
What does the p value measure?
The strength of evidence against the null hypothesis
What does a small p value indicate?
The test statistic is very unlikely to occur when the null hypothesis is true
What can we do when the p value is very small?
Reject H0 in favour of H1
