← VCE Data Analysis

Data quality: bias

Data that unfairly favours one view or group because of how it was collected or selected, e.g. sampling bias, leading questions or missing groups.

Part of: VCE Applied Computing - U1O1 - Data analysis — Module 29, VCE Data Analytics - U3O1 - Data Analytics — Module 140, ACARA Digital Technologies Years 7–8 — Acquiring and Storing Data — Module 11, ACARA Digital Technologies Years 9–10 — Acquiring and Validating Data — Module 87

Understanding Data quality: bias in VCE Data Analysis

What it does: Leaving out students without home internet means a whole group is missing, so the data favours those who are online and is biased. A leading question pushes people towards a certain answer. The neutral rating question lets students give their own view. This is the core idea of bias. The problem comes from the way the data was collected or selected, not just from random mistakes. Leaving out groups, such as people who dislike the app or never used it, makes the data favour satisfied users. Asking only one year level leaves out other groups, so the results do not represent the whole school. Including all year levels reduces sampling bias.

Common mistakes: A random sample gives every student an equal chance of being picked, so the risk of sampling bias is low. It should be: bias risk ← LOW. This is a leading question because it assumes the app is easy and pushes the answer. A neutral version is: Q3 ← How easy is it to use?

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This module's key terms are also in a printable crossword (Modules 25–37) and word search (Modules 25–54).

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Learning
Duo
A school surveys only students in the library at lunch about how much they enjoy studying. Is the data likely to be biased?
No, because any students who answer make the data fairYes, it is biased because it only samples students who choose to be in the library
Matches
Q: "Don't you agree the new timetable is terrible?"
↓
This is a leading question. The wording pushes respondents to agree, so the data is biased. It should be neutral, such as: "How would you rate the new timetable?"
Applying
Meanings
Term
biased data
Meaning
Data that unfairly favours one view or group because of how it was collected or selected, e.g. sampling bias, leading questions or missing groups.
Practice
=COUNTIF(B2:B101,"Year 12")/COUNTA(B2:B101)
Testing
Gaps
Data that favours one group is
Check Answer
Spots
2sample ← 40 chosen at random
3bias risk ← HIGH

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Quick Questions

1. A school surveys only students in the library at lunch about how much they enjoy studying. Is the data likely to be biased?
A. No, because any students who answer make the data fair
B. Yes, it is biased because it only samples students who choose to be in the library ✓
This is sampling bias. Students in the library are not a fair sample of the whole school, so the results favour one group.
2. Which survey question is a leading question that creates biased data?
A. "Don't you agree that our amazing canteen has great food?" ✓
B. "How would you rate the canteen food from 1 to 5?"
A leading question pushes people towards a certain answer. The neutral rating question lets students give their own view.
3. Biased data unfairly favours one view or group because of how it was collected or selected.
A. True ✓
B. False
This is the core idea of bias. The problem comes from the way the data was collected or selected, not just from random mistakes.
4. A company surveys customers about a new app, but only by emailing people who already use the app. What is the main problem?
A. The data is too quantitative to be useful
B. Missing groups: people who stopped using or never tried the app are left out ✓
Leaving out groups, such as people who dislike the app or never used it, makes the data favour satisfied users.
5. Which sample is LESS likely to give biased data about the music tastes of all Year 10 students?
A. Randomly selecting students from every Year 10 class ✓
B. Asking only the members of the school band
A random sample from all classes gives everyone a fair chance. Band members are likely to share similar tastes, which creates sampling bias.

Match the Pairs

Sampling bias → The data comes from a sample that does not fairly represent the whole group, such as surveying only people at a gym about fitness habits.
Leading question → A survey question worded to push people towards a particular answer, which makes the responses unfairly favour one view.
Missing groups in the data make the results unfair because some people's views are never recorded. → Survey run online only, so students without internet at home are left out
Biased data unfairly favours one view or group because of how it was collected or selected. → Poll about school canteen food only given to the canteen's regular customers
Q: "Don't you agree the new timetable is terrible?" → This is a leading question. The wording pushes respondents to agree, so the data is biased. It should be neutral, such as: "How would you rate the new timetable?"
Sample: 50 Year 12 students asked about the whole school's study habits → Other year levels are missing from the sample, so it is biased. It should include a mix of students from every year level.

Key Term

biased data
Data that unfairly favours one view or group because of how it was collected or selected, e.g. sampling bias, leading questions or missing groups.

Fill in the Blanks

1. Data that favours one group is biased
Hint: Type the word for data that unfairly favours one view or group.
2. =COUNTIF(C2:C99,"Yr 12")/COUNTA(C2:C99)
Hint: Type the function that counts all non-empty cells, giving the total responses used to check how well a group is represented.
3. Q: "Don't you agree pizza is the best?" Problem: leading question
Hint: Type the word for a question that pushes the person towards a particular answer.
4. Surveying only your friends is sampling bias
Hint: Type the kind of bias caused by how the people in the data were selected.
5. IF Year12Count = 0 THEN Biased = true
Hint: Type the Boolean value that shows the data has a missing group and is biased.

Spot the Error

Question 1
A population ← 800 students
B sample ← 40 chosen at random
C bias risk ← HIGH
Line C — A random sample gives every student an equal chance of being picked, so the risk of sampling bias is low. It should be: bias risk ← LOW
Question 2
A survey ← app feedback
B Q1 ← Rate the app (1-5)
C Q2 ← How often do you use it?
D Q3 ← Why is it so easy to use?
Line D — This is a leading question because it assumes the app is easy and pushes the answer. A neutral version is: Q3 ← How easy is it to use?
Question 3
A goal ← views of all Year 11s
B groups ← Class 11A only
C ask ← each group
Line B — Only surveying one class leaves the other Year 11 classes out, so groups are missing from the data. It should include all classes: groups ← all classes
Question 4
A topic ← school start times
B population ← all students
C sample ← my friends only
D bias risk ← low
Line C — Choosing only friends is a convenience sample that does not represent the whole population, which causes sampling bias. It should be a random pick from the roll.
Question 5
A target ← all local residents
B contact ← landline phone only
C record ← every response
Line B — Landline-only contact misses people who only use mobiles or the internet, so those groups are missing from the data. Use more than one method: phone and online.

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