11-Estimating the Difference Between the Means of Independent Populations Flashcards
What is a a hypothetical population?
one that does not exist, but which could exist. Individuals in an experimental group that undergo a novel treatment can be considered a sample from a hypothetical population of all individuals that undergo the same treatment.
What are Independent samples?
comprise scores that are completely unrelated to each other. This means that knowing the score of an individual in one sample tells you nothing about the score of any individual in the other sample.
What are Dependant samples ?
comprise scores that are related to each other in some way; either pairs of scores come from the same individual (repeated measures) or pairs of scores come from individuals matched on some characteristic (matched samples).
what is the formula for estimated standard error ? (sm1-m2)?
sqart of (s2 1/n+s2 2/n)
What is the formula for the standard error of m1-m2 ?
sqrt of (o2 1/n1) + (o2/n2)
What is the formula for t distributions of m1-m2 ?
t= (m1-m2)-(u1-u2)/ sm1-sm2
What is the formula for s2 pooled ? What is the formula for w ?
w1(s2 1)+ w2 (s2 2)
df / df within
df withon (df1+df2)
What is a weighted sum ?
a way of computing the mean of two or more statistics by multiplying each statistic by a weight related to sample size and then summing the products.
What is the formula for s2 pooled when ss is given ?
ss1+ss2/df within
How to compute the estimate of effect size?
d=m1-m2/s pooled
*s pooled the square root of s2 pooled
What is the for furmula for the approximate estimated standard error of d when we have two samples and o is unknown ?
sqart of (d^2/2*df)+ (1/n1)+ (1/n2)
What is r2 ?
It represents the proportion of variance in the merged group of scores that is attributable to the difference between the two group means.
What is the formula for within group variablity ?
ss1+ss2=sswithin
what is the formula for between group variability ?
sstotal-sswithin=ssbetween
What is the formula for r2 ?
ssbetween/sstotal
