lecture 4: statistical inference - comparing two groups

Question 1

true/false: the variance of the difference (or the sum) of the 2 individual random variables equals the sum or the variances of the two populations from which the samples were drawn

Answer 1

true

Question 2

assuming sample sizes are equal n1=n2 the variances can be averaged for greater precision to create a _________ variance

Answer 2

pooled

Question 3

what is the formula of pooled variance

Answer 3

(variance of sample one + variance of sample 2)/2

Question 4

for 2 samples of ______ (same/different) sizes n1 does not = n2, the pooled variance is calculated as a weighted average

Answer 4

different

Question 5

what are the assumptions needed for a two sample t test

Answer 5

1. random sampling
2. indépendant samples
3. sampling from normally distributed populations
4. homogeneity of variance

Question 6

does this describe a one tailed or two tailed test?
looks for an “increase” or “decrease” in the parameter

Answer 6

one tailed

Question 7

does this describe a one tailed or two tailed test?
looks for a “change” (could be increase or decrease) in the parameter.

Answer 7

two tailed

Question 8

this type of error occurs when the null hypothesis is rejected, when in fact, it is true; the probability of committing this type of error is usually set at 5%

Answer 8

type I (alpha error)

Question 9

this type of error occurs when the null hypothesis is not rejected, when in fact it is false; the probability of committing this type of error is set maximally at 20%

Answer 9

type II (beta) error

Question 10

which is worse, a type I or type II error?

Answer 10

type I because your saying something that doesn’t work, works

Question 11

we can test for ________ by examining the ratio of the sample variance and if the quotient is less than 0.5 or greater than 2 then we need to perform a separate variance t-test

Answer 11

homogeneity