UNIVERSITY OF PRETORIA
Theme 1: Introduction to data
Presenter: TM Malatji
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Welcome
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Assistant Lecturer: Mr. Henry Schnetler
3 Lecture periods – 2 Online, 1 Physical
Attend according to your group
All queries to BES220info@gmail.com
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Contents
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General process of investigation
Purpose of statistics
Case study
Observations
Variable types
Relationship between variables
Study types
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Theme 1: General process of
investigation
1. Identify a question or problem.
2. Collect relevant data on the topic.
3. Analyze the data.
4. Form a conclusion.
Statistics focusses on making steps 2, 3 and 4
objective, rigorous and efficient.
1. How best can we collect data?
2. How should we analyze the data?
3. What can we infer from the analysis?
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Theme 1: Purpose of statistics
1. Data collection is done objectively
Example: In 2007, Colgate was ordered by the Advertising
Standards Authority (ASA) of the U.K. to abandon their claim: “More
than 80% of Dentists recommend Colgate.” The slogan in question
was positioned on an advertising billboard in the U.K. and was
deemed to be in breach of U.K. advertising rules.
What went wrong?
1.
2.
A survey was sent out to dentists and hygienists and only those
who responded were sampled – Not a random sample and not
representative of all dentists.
The survey allowed respondents to select more than one
toothpaste – Not recommending the product.
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Theme 1: Purpose of statistics
2. Data is analyzed rigorously
Example: A researcher conducted a study in which ice cream
sales for a 5 year period and forest fires in that same period were
studied. The researcher observed that ice cream sales and forest
fires are directly proportional (both increase/decrease concurrently)
and concludes that ice cream consumption leads to more forest
fires.
What went wrong?
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Ignoring important features – The study did not consider other
confounding variables that could be related to both variables,
e.g. the weather is related to both variables and could be the
cause for the high ice cream sales and the increase in forest
fires.
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Theme 1: Purpose of statistics
3. Conclusions are formed correctly
Example: A professor wants to know which lecture period is
most preferred by students at the university. She samples 100
students from her class and asks them to select a lecture period
that they prefer most and she ends up with a list of 3 most preferred
lecture periods. She then presents to the HOD of her department
that students generally prefer the 3 lecture periods that she found.
What went wrong?
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Generalizing the results to a larger group – Her students are
not a representative sample of the population and she didn’t
study any other groups, so she can’t draw conclusions about all
students in the department.
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Theme 1: Case study - Using stents
to prevent strokes
• Research question:
– Does the use of stents reduce the risk of
stroke?
• Data on 451 at-risk patients collected
• Each volunteer patient randomly assigned to
treatment or control group.
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Theme 1: Case study - Using stents
to prevent strokes
• A summary statistic is a single number that
summarizes a large amount of data.
• Proportion who had a stroke in the treatment
group: 45/224 = 20%
• Proportion who had a stroke in the control
group: 28/227 = 12%
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Theme 1: Case study - Using stents
to prevent strokes
• Difference of 8% with less strokes in control
group.
• Is this 8% significance or due to chance?
– We will learn how to test the significance of
our results.
• Can we generalize these results to all stroke
patients and all stents?
– We will learn when we can make causal and
correlation statements.
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Theme 1: Observations
• Data matrix contains the observation data
• Case is a single row in the data matrix
• Variables are the characteristics under study
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Theme 1: Variable types
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Theme 1: Variable types
• Numerical variables:
– Discrete
• Whole, non-negative numbers
• Example: The number of cars on the
highway at a point in time
– Continuous
• Infinite range of number values
• Example: The size of a plot of land in
square meters
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Theme 1: Variable types
• Categorical variables:
– Categorical
• Non-numeric with no specific order
• Example: Countries in the African
continent
– Ordinal
• Non-numeric with a natural order
• Example: Top 5 contestants in a singing
competition
• Example: Satisfaction levels of customers
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Theme 1: Relationship between
variables
• Relationship:
– Associated
Hours of sleep
Sleep hours required as a function
of age
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10
15
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Age
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Theme 1: Relationship between
variables
• Relationship:
– Independent
Income as a function of weight
Monthly income (R1000)
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70
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40
60
Weight (kg)
80
100
120
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Theme 1: Relationship between
variables
• Describing relationship:
– Direction (Positive/Negative)
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Theme 1: Relationship between
variables
• Describing relationship:
– Form (Linear, non-linear or detail)
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Theme 1: Relationship between
variables
• Describing relationship:
– Strength (Strong, Moderate, Weak)
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Theme 1: Relationship between
variables
• Describing relationship:
– Direction (Positive/Negative)
– Form (Linear, non-linear or detail)
– Strength (Strong, Moderate, Weak)
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Theme 1: Relationship between
variables
• Explanatory variable
(Independent):
– Suspected to cause
effect in response
variable.
• Response variable
(Dependent):
– Suspected to respond to
changes in explanatory
variable
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Theme 1: Study types
• Observational study:
– A study in which cases are observed or
outcomes are measured without any
intervention to affect the outcomes (e.g. No
treatment given).
• Experimental study:
– A study in which an intervention is introduced
and the effects are studied.
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Theme 1: Study types
• A study took a random sample of people and
examined their social media habits. Each
person was classified as either a light,
moderate, or heavy social media user. The
researchers looked at which groups tended to
be happier.
– Observational or Experimental study?
• Observational
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Theme 1: Study types
• A study took a group of adults and randomly
divided them into two groups. One group was
told to drink tea every night for a week, while the
other group was told not to drink tea that week.
Researchers then compared when each group
fell asleep.
– Observational or Experimental study?
• Experimental
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Theme 1: Week 1 L1 Summary
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General process of investigation
Purpose of statistics
Case study
Observations
Variable types
Relationship between variables
Study types
PS: Do complete the homework as exercise
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Thank you!
Happy studying 
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