STATS5- Student’s t-distribution

when are t-distributions used

• when sd from parent population is unknown

• can’t use a z-score

2 similarities between t-distribution curve & normal distribution curve

• bell-shaped

• uni-modal

2 differences between t-distribution curve & normal distribution curve

• t-distribution peak is smaller

• t-distribution has heavier/higher tails

V in t-distributions

• n-1

• when v decreases graph looks less like normal distribution

how to work out t-score

m= given value

what column do you use for 1 tailed t-distribution table

0.025 (0.025×2=0.05)

what column do you use for 2 tailed t-distribution table

0.05

how to work out 95% confidence interval for t-distributions

what tail significance do you use for t-test confidence intervals

2-tailed

what tail significance do you use for standard t-tests

1-tailed

what do you interpret if p value is bigger than critical value for a t-test

p<0.05 (reject the null hypothesis)

what do you interpret if p value is smaller than critical value for a t-test

p>0.05 (fail to reject the null hypothesis)