1- and 2-sample t-tests Flashcards
1
Q
The smaller the sample size is…
A
- the more variable the sample SD is as an estimate of σ
- hence the distribution of the test statistic will be “wider”
2
Q
The t-distribution with v degrees of freedom
A
- v = ∞ results in the standard normal distribution
- The standardised chance error (if standardised with the sample SD) follows a t-distribution with v = n−1 = sample size − 1
3
Q
The “best” choice of weighted average is the one that…
A
Gives the resultant estimate the smallest possible SE.
4
Q
Assumptions for 2-sample t-test
A
- All observed individuals are independent
- The two samples contain different people
- The two populations are normal and have equal spread (SD/var)
5
Q
var.equal = for t.test
A
T - indicates we are doing 2-sample
F - would run a Welch t-test
6
Q
We can relax the assumption that 2 pop. have to have equal spread by using a…
A
Welch 2-sample t-test
7
Q
One-sample t-test
A
Looks at diff between sample mean and a fixed value
8
Q
Two-sample t-test
A
Looks at the diff between sample means from 2 diff group
* Take the difference and see if it is 0
9
Q
z-test
A
Diff between a population proportion and fixed proportion value
10
Q
95% CI’s for population proportion
A
CI= ov ± se x qnorm(0.975)
