Transcript stats_centraltendency, graphs e.t.c

Trying an Experiment
BATs
Conduct a memory experiment with real
participants in a professional and ethical
way
Collect data
• Have
you got all your materials ready?
• We will be testing year 11 students period 1
• After we have collected the data we will analyse
it back in HU7 or the Bath Spa room.
Descriptive Statistics
BATs
 Use measures of central tendency (mode,
median and mean)
 Analyse the advantages and
disadvantages of each type of descriptive
statistics.
 Draw graphs and interpret data from real
experiments
Descriptive Statistics
 Measure of central tendency
 Gives a typical value for the data set
 Tells you where the middle of the data set is
 Indicates how the data are spread out
 Tells you what the rest of the data are doing
www.psychlotron.org.uk
 Measure of dispersion
Descriptive Statistics
an accurate summary of the data
 The wrong choice of statistic gives a
distorted picture of the data
 This can lead to the wrong conclusions
being drawn from the data
 Each measure of CT and D has its
advantages and disadvantages
www.psychlotron.org.uk
 The aim of descriptive statistics is to give
Measures of Central Tendency
 The mean
 Use it when the data are normally
distributed, unskewed and there are no
outliers
www.psychlotron.org.uk
 Adv: it uses all the values in the set, so is
most sensitive to variations in the data
 Dis: it can be artificially raised or lowered by
an extreme value, or by skewed data
Measures of Central Tendency
 Adv: it is based on the order of the data, not
their actual values, so not distorted by
extreme values
 Dis: however, this makes it less sensitive to
variations in the data
 Use it when you can’t use the mean
because of skew, outliers etc.
www.psychlotron.org.uk
 The median
Measures of Central Tendency
 The mode
 Use when dealing with frequency data,
and/or where there is a clear modal value
in the set
www.psychlotron.org.uk
 Adv: it’s the only measure suitable for
summarising category/frequency data
 Dis: for many data sets there is no modal
value, or their may be several
Which stats would you choose?
 In groups of 3 read the ‘Choice of
Statistics worksheet
 Discuss q 1 and 2 – which measure of
central tendency would be best for each
list of data?
1. Should have chosen the colour that was picked most
often – the mode
a. Mean, b. mode, c. mean or median ( numbers in order),
d. mode, e. Median (mean not best because a few
outliers)
Measures of Dispersion
 Range:
 Simple measure of dispersion- shows the
total spread of data.
 Difference between highest and lowest
scores in a set of data: top value minus
bottom value plus 1.
 Affected by atypical, extreme values.
 Interquartile ranges can also be used
see p 119 Exploring Psychology
Measures of Dispersion
 Standard Deviation:
 Measure of dispersion- shows degree of
clustering of values around the mean.
 Calculating standard deviation (S): Square
root of sum of all squared deviations from
the mean, divided by N (or sometimes N1).
 The smaller the sd the closer the scores
are to the mean, high sd = scores spread
out a long way from mean.
Measures of Dispersion
 Standard Deviation:
 The most accurate measure of
dispersion –
 It is more precise than range because all
values are taken into account
 BUT … have to calculate it – time
consuming
Displaying Data
 Tables – clear headings with units of
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measurement
Graphs – see findings at a glance
Bar chart – discrete categories, bars separated
Histogram – x axis has continuous data, no
gaps between bars (DV on x axis, frequency on
y axis)
Line graph/frequency distribution curve e.g
Yerkes- Dodson curve
What type of graph?
What types of graph are used in each of the
following…
 Murdock (1962) p16
Frequency distribution
curve
 Van Ijzendoorn and Kroonenburg (88)
p57/8
Bar chart
Plenary
 Answer the questions 1, 4,5,6 and 7
 Use the answer sheet to mark your
answers
Using your own data
BAT
Draw graphs and interpret data from your
own experiment
Evaluate the work of others
Over to you
 Select the most appropriate descriptive
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stats for your data (central tendency and
dispersion) and calculate
Display your data in a graph of your
choice
What does your data tell you?
Will you accept or reject your hypothesis?
How could you improve your method?
Peer Review
 Before a piece of Psychological research
can be accepted it is reviewed by other
psychologists to check the work’s validity
and reliability.
 Read the method, and data analysis of
someone in a different group.
 Would you accept their work?
 How could reliability and/or validity be
improved
Plenary and Homework
 Homework – complete the worksheet by
next lesson
 Start to Revise for Mock exam – use the
blog quiz!! The results will be emailed to
me