making decisions Flashcards
z score
measure of distance between the sample statistic and population parameter
how to decide exact probability that sub group and pop have same mean
use normal tables
what z score puts the sample in the rarest 5%
equal or more than 1.96
what z score puts the sample in the rarest 1%
equal to or exceeds 2.58
alpha level
risk we are willing to take that we reject null hypothesis when its really true
alpha level of 5% =
a score 1.96 (5% risk we are wrong)
alpha score og 1% =
z score 2.58 (1% risk we are wrong)
why not increase level of significance
would increase number of times we accept null when we should reject it
type 1 (alpha) error
reject null but should be accepting it
type 2 (beta) error
fail to reject null but its not actually true
z test
comparing z scores to a critical value
2 tailed test / non directional
reject null if sample statistic reaches critical value in either tail
1 tailed test / directional test
when association can only be one direction we allocate 5% risk of error to one side of distribution
when are parametric assumptions used
only for ratio / interval data
what to do when the population size is less than 30 or don’t have the pop SD
t test or sign test
