Transcript Quantitative Data Analysis - PsychologyResources-Y13

Quantitative data analysis
In plain English
Need to know
• Information collected in study called “data”
• Numerical data are called “quantitative”
• Levels of data
– Nominal
– Ordinal
– Interval
– Ratio
Mnemonic technique (acronym)
to remember these: NOIR
Levels of data: Nominal
• Data goes into categories.
• Can only be used as frequencies.
• Example: Which newspaper paper do you
read regularly?
Levels of Data: Ordinal
• Data can be put in order… highest to
lowest
Finish line
Example: What grade
did you get for each of
your gcse’s?
Example: Races
Levels of data: Interval
• Data are measured using units of equal measure
Example:
How anxious are you?
1
2
3
4
5
6
7
8
9
10
Levels of data: Ratio
•Must have all properties of interval data
•There is also a true zero point
Reaction times: We can measure and compare
the exact time because there is an absolute zero
point (0 seconds).
Example: How quick is your reaction time?
Measures of central tendency
Tell us about a ‘typical’ response for a data set
o Mean – average (add up all the values and divide
by the total number of values)
o Median – middle value
o Mode – value that is most common
Mean
Median
Mode
-Cannot be used with
nominal data sets
- Not good if too many
extreme values
-Uses all the values
-Not as affected by
extreme scores
-Not as ‘sensitive’ as
the mean
-Useful with nominal
data
-Not useful if there are
several modes
Measures of dispersion
Describes how spread out the data is
o Range – lowest to highest
3, 5, 8, 8, 9, 10, 12, 12, 13, 15
1, 5, 8, 8, 9, 10, 12, 12, 13, 17
Range = 12 (3-15)
Mean = 9.5
Range = 16 (1-17)
Mean = 9.5
Measures of dispersion
o Standard deviation – shows amount of
deviation in a set; describes data around the
mean.
Visual Displays: Tables
• Numbers you collect, untreated “raw data”
• Can be summarized using mean, median, mode
3, 5, 8, 8, 9, 10, 12, 12, 13, 15
1, 5, 8, 8, 9, 10, 12, 12, 13, 17
Visual Displays: Bar Chart
• Shows frequency
• Can be used with
nominal data
(categories) or
numbers
Visual Displays: Line Graph
• Y-axis shows
frequency
• X-axis Cannot use
with nominal data
(categories)
Visual Displays: Scattergram
• Graph used with
correlational analysis
(we’ll look at this
later!!)
Practice!
Fakedata and Fraud (2004) carried out an investigation to
decide what colour to paint the walls of their Psychology
department. They assigned each possible colour to a
number (white=1, green=2, brown=3, red=4 etc.) and then
carried out a survey to see which colour the staff and
students would prefer. Once they had asked everyone
their preference, they decided on the final colour by
calculating the mean of all the colour values to find an
average colour that everyone would like. The mean came
out at 3.1, so the researchers painted the department
brown. Everyone hated it.
1. Explain where Fakedata and Fraud went wrong, referring
to their choice of measure of central tendency in your
answer.
More practice
Take a look at each of the following data sets. For each one,
state which measure of central tendency you would choose
to summarise it, and explain why your choice is appropriate.
(a) 1, 3, 4, 4, 7, 9, 10, 10, 12
(b) yes, yes, no, yes, no, no, yes, no, yes, yes, yes, no, no, no, no
(c) 13, 17, 19, 20, 24, 25, 26, 31, 36, 37, 56
(d) 0, 0, 0, 0, 0, 0, 0, 12, 14, 17, 20
(e) 3, 21, 25, 26, 30, 32, 32, 35, 36, 45, 47, 50
Into groups
Group A:
Question 2: Why is it better to
know about the mean and range
of a data set rather than just the
mean?
Also Data Set 1 (Question 1)
Group B:
Question 3: Explain why it might be
better to know the standard deviation
of a data set rather than the range.
Group C:
Question 4: Look at the following
data sets. Which one do you think
would have the smaller standard
deviation?
2 2 3 4 5 9 11 14 18 20 21 22 25
2 5 8 9 9 10 11 12 14 15 16 20 25
Group D:
There are three graphs on page 81.
a. What can you conclude from graph
C?
b. Write a title that would be suitable
for all three graphs.
c. Describe the y axis of all three
graphs.
Also Data Set 4 (Question 1)
Also Data Set 3 (Question 1)
Also Data Set 2 (Question 1)