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MCD6110
Psychology 1B
Lectures 1 & 2, Week 8
Psychological Discovery:
Summarising Data Using
Descriptive Statistics
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Learning Outcomes W7, L1 & L2
1.Distinguish between descriptive and inferential statistics;
2.Organise and summarise data in the form of frequency distribution
tables and graphs;
3.Calculate and differentiate between the three measures of central
tendency (mean, median, and mode);
4.Describe and calculate measures of variability or dispersion (range,
variance, standard deviation);
5.Describe the position of a particular score in a distribution using z-
scores; and
6.Summarise the properties of the standard normal distribution and its
relationship with probability.
3
2. Form a
Hypothesis
3. Define and
Measure
Variables
4. Identify
Participants or
Subjects
5. Select a
Research
Strategy
6. Select a
Research
Design
7. Conduct the
Study
8. Evaluate the
Data
9. Report the
Results
10. Refine or
Reformulate
Research Idea
1. Find a
Research Idea
Research Methods for the Behavioral Sciences, Fourth
Edition by Frederick J Gravetter and Lori-Ann B. Forzano
Copyright © 2011 Wadsworth Publishing, a division of
Cengage Learning. All rights reserved.
Conducting the Study
▪ Recruit the participants
▪ Apply your measurement procedures
▪ Collect the data!
5
6Descriptive Statistics
▪ After we have collected our raw data, we need to reduce the endless list
of numbers into a manageable and meaningful summary. This is called
descriptive statistics.
▪ Descriptive statistics entail the organisation, summarisation, and
simplification of raw data so that patterns and trends in variables can
be seen
– i.e., making order out of chaos!
7Descriptive vs. Inferential Statistics
▪ Descriptive statistics are methods for simplifying, organizing and
summarizing data
– Note that a descriptive value for a population is called a
parameter (symbolised by Greek letters, μ, σ, σ2, etc.) and a
descriptive value for a sample is called a statistic (symbolised by
regular (English) letters, M, s, s2, etc.)
▪ Inferential statistics are methods for using sample data to make
general conclusions (inferences) about populations.
– i.e., sample statistics are used as the basis for drawing
conclusions about population parameters
▪ A frequency distribution is an organized tabulation showing exactly
how many individuals are located in each category on the scale of
measurement
▪ A frequency distribution presents an organized picture of the entire set
of scores, and it shows where each individual is located relative to
others in the distribution
– i.e., how did each individual score in relation to the rest of the
group