Stats semester 2

Question 1

What is estimated standard error?

Answer 1

s / root N

Question 2

how do you work out t?

Answer 2

t = (m-u) / s/rootN

v = N - 1

Question 3

what is effect size (d)?

Answer 3

measure of difference in means taking into account the sd

d = (u1 - u2) / meanSD

meanSD = (theta 1+2)/2

Question 4

how do you do a related paired t test?

Answer 4

find chance (post - pre) and do a normal t test.

Question 5

what is the null hyporthesis for finding the difference between 2 populations?

Answer 5

mean A = mean B

Question 6

what is variance?

Answer 6

sd ^2

Question 7

what is t for an independent t test?

Answer 7

t = (mA – mB) / √( [SA2/nA] + [SB2/nB])

Question 8

what is v for an independent t test?

Answer 8

(nA-1)+(nB-1)

nA+ nB-2

Question 9

how can you measure correlation?

Answer 9

pearsons r

spearmans rho

Question 10

describe pearsons r

Answer 10

allows us to conduct a parametric test to decide
whether there’s a real relationship between
variables (or if its quite likely that observed data
could have arisen just by chance)

Question 11

describe covariance and sample covariance.

Answer 11

Covariance describes how much two variables co-vary
(the amount of variance they share).

sample covariance (C) is given by C = TC/(N-1)

Positive covariance - indicates that higher than average values of one variable
tend to be paired with higher than average values of the other variable.
– Negative covariance - indicates that higher than average values of one variable
tend to be paired with lower than average values of the other variable.
– Zero covariance - if the two random variables are independent, the covariance
will be zero. However, a covariance of zero does not necessarily mean that the
variables are independent. A nonlinear relationship can exist that still would result
in a covariance value of zero.

Question 12

how do you work out r in pearsons r?

Answer 12

r = covariance/total individual variance.
between -1 and 1

r = c/ SxSy
r = c/ sdx sdy

Table is set up for you to simply look in row N
V = N-2
???

Question 13

what is the difference between pearsons r and a p value?

Answer 13

Pearson’s r tells you the strength/direction of the
relationship between variables
– The p-value tells you the probability that this correlation
coefficient could arise by chance assuming the null
hypothesis is true

A large Pearson’s r DOES NOT tell you that there is necessarily a
correlation between your variables

Question 14

when do you use the 1 variable chi squared test?

Answer 14

We use this when we have one categorical variable
with at least 2 categories.

Used when we want to assess whether observed
frequencies in each category different from what is
expected

Question 15

what does the chi squared test tell us?

Answer 15

the chi-square statistic tells us about
whether observed frequencies depart from what is
expected (which will be known).

Question 16

equation for chi squared?

Answer 16

sum (E-O)^2 / E
(E-O) = sum of difference

1 variable - V = C-1
2x2 V = (C-1)x(R-1)

Question 17

2x2 cell chi squared test?

Answer 17

expected =
multiply totals of column and row / grand total

then use sum (E-O)^2 / E

Question 18

what are the non parametric tests?

Answer 18

spearmans rho (r)
mann whitney and wilcoxon (t)

Non-parametric test are less powerful than their parametric
friends… but they are assumption free

Question 19

how do you rank numbers?

Answer 19

remember equal values become the mean of the rank

Question 20

how do you do spearmans rho?

Answer 20

Convert scores to ranks
• Calculate difference in
ranks
• Square the difference

equation?

Question 21

when do you use wilcoxon and mann whitney?

Answer 21

Wilcoxon signed rank test (Wilcoxon) is an
alternative for the paired/related t-test

The Mann-Whitney U test (Mann Whitney) is an
alternative for the independent t-test

Question 22

how do you do a mann whitney test?

Answer 22

rank regardless of condition, then find mean of each condition.

mann whitney tells us if difference in mean rank is significant.

Question 23

how do you do a wilcoxon test?

Answer 23

calculate difference (after - before).
rank the non zero difference scores, ignore signs but take ties into account.

Question 24

how do you work out shared variance from r?

Answer 24

r^2