[L7] Data from Independent Groups: Categorical Measures

Question 1

– can only take on one of a
limited number of values, often simply yes or no.

Answer 1

Categorical or Nominal data

Question 2

– very rarely used as an appropriate measure of
central tendency.
* It does not tell much.

Answer 2

Mode

Question 3

• Three main ways of showing the difference between two
  proportions. (fourth one as well)

Answer 3

Absolute and Relative Change

Question 4

All look very similar to each other and it is often not clear
which one people are talking about.

Answer 4

Absolute and Relative Change

Question 5

• We usually describe the % of people in each group and the
  differences between them.
• We also get on to the 95% CIs.

Answer 5

Summary Statistics

Question 6

• Third way of showing the difference two proportions.

Answer 6

Odds Ratio

Question 7

Trickier than percentages and proportions but most
common way.

Answer 7

Odds Ratio (OR)

Question 8

Odds are always presented as

Answer 8

“something to one”.

Question 9

First way is to look at the data is to use the

Answer 9

Absolute
Difference

Question 10

The___ in the percentage of people who
took the antibiotic is 15%.

Answer 10

absolute reduction

Question 11

Reduction in antibiotic use as a ___ of those in
the leaflet group

Answer 11

Proportion

Question 12

So giving a leaflet reduces the chances that the person
will take antibiotics by 24%. This is the ____

Answer 12

Relative Risk
Decrease.

Question 13

As a relative probability of taking the medicine, as a
proportion of those who would have ___

Answer 13

taken the medicine.

Question 14

What are the odds of throwing a 6 on a die
/dice? Tricky because it is…

Answer 14

counter-intuitive

Question 15

The odds are 5 to 1, or 5: 1. The event will not
happen___ that it does happen.

Answer 15

5 times for each time

Question 16

If we know the ____, p, we can calculate the odds
using the following formula:

Answer 16

probability

Question 17

Chi-square

Answer 17

Odds Ratio

Question 18

Easier way of calculating the odds ratio.

Answer 18

OR = AD / BC

Question 19

OR = AD / BC

Answer 19

distribution of frequency scores

Question 20

• One more method of presenting the effect of an
  intervention which is commonly used in medicine,
  though less commonly used in psychology

Answer 20

Number Needed to treat (NNT)

Question 21

Also known as NNH or

Answer 21

number needed to harm.

Question 22

The NNT is very easy to calculate. It is simply

Answer 22

• NNT = 1 / Absolute Risk Difference

Question 23

• Although it is possible to compute for all the descriptive
  statistics that we calculated, most of them are rarely used
  so the only one we are going to concentrate on is the
  \

Answer 23

odds ratio.

Question 24

v, (Greek
letter nu, pronounced ___

Answer 24

“new” or “noo”)

Question 25

v is a bit like the ___of the odds ratio

Answer 25

standard error

Question 26

Odds ratio

Answer 26

raw score

Question 27

t-test

Answer 27

standardized score (d)

Question 28

convert OR to ____, to know if its difference is significant

Answer 28

chi-square

Question 29

• Developed by Pearson and sometimes known as the
  Pearson χ² test.

Answer 29

Chi-Square χ²

Question 30

The first stage in the χ² test is to put the ___

Answer 30

values into a
table, but add totals to it.

Question 31

• We have to calculate the ___for each cell,
  which are referred to as ___.

Answer 31

expected values , E

Question 32

The E are the values that we would
_
__,

Answer 32

expect if the null
hypothesis were true

Question 33

The expected values are given by:
__

Answer 33

• E = R x C / T

Question 34

Where R refers to the___, C the ___, and T for____

Answer 34

total for a given row; total
for a given column; grand total.

Question 35

O = ___

Answer 35

Observed value

Question 36

All we need to know is the ____so we can take
the differences and add them up. (Almost but not quite)

Answer 36

distance between the
observed value and the expected value

Question 37

The difference needs to take account of the___

Answer 37

sample size

Question 38

χ² = Σ (O - E)² / E

Answer 38

similar, deviation score

Question 39

An assumption made by the χ² test is that all of the
expected values (in a 2 x 2 table) must be ___

Answer 39

greater than 5.

Question 40

chi-square critical value, sample

Question 41

Degrees of Freedom (df)

Answer 41

• df = (number of rows – 1) x (number of columns – 1)

Question 42

If the table is larger than 2 x 2, then __ of the expected
values need to be above
__

Answer 42

80%; 5.

Question 43

If our data do not satisfy this assumption we can use the
___ instead.

Answer 43

Fisher’s exact test

Question 44

2nd, when we have a 2 x 2 table the χ² test is a little bit
__, and statisticians do not like liberal tests

Answer 44

liberal

Question 45

A
__- is slightly more prone to say that a result is
statistically significant than it should be, so the Type I
Error rate is not 0.05, but a little bit higher than that

Answer 45

liberal test

Question 46

One approach in dealing with this is to use ____

Answer 46

Yates’
Correction for Continuity or Continuity Correction

Question 47

The values contained within the bars means ___, which means if there is a minus sign
ignore it.

Answer 47

“take the
absolute value”

Question 48

The problem with Yates’ correction is that it makes the
test a little conservative so the ___is now
___

Answer 48

Type I Error rate; smaller than 0.05

Question 49

This in itself is not a problem, but it means that the test is
now ___, when it
should be giving one

Answer 49

less likely to give a significant result

Question 50

In fact, the correction only matters when the sample size
is ____

Answer 50

relatively small.

Question 51

So if the sample size is __, the correction makes little
difference.

Answer 51

large

Question 52

If the sample size is small, there is a better test we can
use called the
____

Answer 52

Fisher’s Exact test.

Question 53

The Idea of Fisher’s exact test is that for some events we
can work out the exact probability of them occurring
without needing to use ___

Answer 53

test statistics and tables.

Question 54

We can do the same thing for data which are in a___

Answer 54

2 x 2
contingency table.

Question 55

Fisher’s exact test gives the probability of getting the
___

Answer 55

exact result that was found in the study.

Question 56

However, we are not just interested in the exact result,
we are interested in any result that is ___

Answer 56

more extreme than
the result we have.

Question 57

Fischer, inspired by __, that led him to form a formula because his wife has a special talent to exactly pin point is a tea is made with tea first or tea

Answer 57

wife