← VCE Data Analysis

Data quality: accuracy

Data is accurate when it is correct and free from errors, so it matches the real-world fact it records. Typos, faulty measurements and out-of-date values make data inaccurate.

Part of: VCE Applied Computing - U1O1 - Data analysis — Module 28, VCE Data Analytics - U3O2 - Analysis and Design — Module 73, VCE Data Analytics - U4O1 - Development and Evaluation — Module 84, VCE Data Analytics - U4O2 - Cyber Security: Data Security — Module 20, ACARA Digital Technologies Years 7–8 — Acquiring and Storing Data — Module 53, ACARA Digital Technologies Years 9–10 — Acquiring and Validating Data — Module 82, QCE Digital Solutions Unit 2 — Data and Programming Techniques — Module 40, QCE Digital Solutions Unit 2 — Prototype Data Solutions — Module 121

Understanding Data quality: accuracy in VCE Data Analysis

What it does: Comparing entered values with a trusted source such as an official report shows whether the data matches the real facts. The data was recorded as measured, but the measurement was wrong, so it does not match the real-world fact. Accuracy is about whether the value is correct. Size and accessibility are different characteristics of data. Consistent readings can still be wrong. Faulty measurements produce inaccurate data. That is the core idea of accuracy. The stored value should be the same as the real fact. Data that was once correct but has not been updated no longer matches reality, so it is inaccurate.

Common mistakes: The typed year (2050) does not match the trusted source (2005), so a typing error has made the data inaccurate. Line 4 should output "Typing error", not say the data is accurate. A large difference from the trusted value signals a measurement error. The condition should be diff > 0.5. Using < flags readings that are actually close to correct.

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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 student types a customer's age as 215 instead of 25. What is the problem with this data?
It is inaccurate because it does not match the real ageIt is accurate because it was entered into the system
Matches
Height (cm): 1750 (should be 175)
↓
A typing error added an extra digit, so the data is inaccurate and must be corrected by checking the source
Applying
Meanings
Term
accuracy
Meaning
Data is accurate when it is correct and free from errors, so it matches the real-world fact it records. Typos, faulty measurements and out-of-date values make data inaccurate.
Practice
=IF(B2=C2,"Accurate","Check for error")
Testing
Gaps
=(B2=Master!B2,"Accurate","Check")
Check Answer
Spots
3IF typed ≠ source THEN
4 OUTPUT "Data is accurate"

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Quick Questions

1. A student types a customer's age as 215 instead of 25. What is the problem with this data?
A. It is accurate because it was entered into the system
B. It is inaccurate because it does not match the real age ✓
A typing error means the stored value no longer matches the real-world fact. Being entered into a system does not make data accurate.
2. Which statement best describes accurate data?
A. Correct and free from errors, so it matches the real-world fact ✓
B. Stored in a large database that many people can access
Accuracy is about whether the value is correct. Size and accessibility are different characteristics of data.
3. A faulty thermometer reads 5°C too high every time. Is the temperature data accurate?
A. Yes, because the readings are all consistent
B. No, the measurement error makes the values incorrect ✓
Consistent readings can still be wrong. Faulty measurements produce inaccurate data.
4. A school's contact list still shows a student's old mobile number after they changed it. What is wrong with the data?
A. It is out of date, so it is no longer accurate ✓
B. It is still accurate because it was correct once
Data must match the real world now. An out-of-date value no longer matches the current fact, so it is inaccurate.
5. How can you check whether a value in a dataset is accurate?
A. Compare it against a trusted source ✓
B. Check that it looks neat and well formatted
Checking against a trusted source, such as an official record, shows whether the value matches the real-world fact. Neat formatting says nothing about correctness.

Match the Pairs

Age: 215 → A typing error: the student meant 15 or 21, so the value does not match the real fact
Address: 12 Oak St (moved in 2019) → An out-of-date value: the person has since moved, so the stored fact is no longer correct
Checking data against a trusted source helps confirm it is accurate → Compare student marks to the official school report
A faulty measuring tool can make data inaccurate even when it is typed in correctly → Scale reads 3 kg when the real weight is 2 kg
Height (cm): 1750 (should be 175) → A typing error added an extra digit, so the data is inaccurate and must be corrected by checking the source
Phone: 0412 345 678 (changed last year, never updated) → The value is out of date, so the data is inaccurate and needs to be updated from a trusted source

Key Term

accuracy
Data is accurate when it is correct and free from errors, so it matches the real-world fact it records. Typos, faulty measurements and out-of-date values make data inaccurate.

Fill in the Blanks

1. =IF(B2=Master!B2,"Accurate","Check")
Hint: Type the function that tests a condition and returns one result if true and another if false
2. IF age < 0 OR age > 120 THEN DISPLAY "Check age" END IF
Hint: Type the logical operator that flags a value if either impossible-age test is true
3. =ABS(B2-C2)<=0.5
Hint: Type the function that gives the size of the difference between a recorded and a trusted measurement, ignoring the sign
4. =IF(A2<>B2,"Typo","OK")
Hint: Type the operator that checks whether two values are not equal
5. =IF(TODAY()-D2>365,"Out of date","Current")
Hint: Type the function that returns the current date so the age of a record can be checked

Spot the Error

Question 1
A source ← 2005
B typed ← 2050
C IF typed ≠ source THEN
D OUTPUT "Data is accurate"
E ENDIF
Line D — The typed year (2050) does not match the trusted source (2005), so a typing error has made the data inaccurate. Line 4 should output "Typing error", not say the data is accurate.
Question 2
A trusted ← 36.6
B sensor ← 38.9
C diff ← ABS(sensor - trusted)
D IF diff < 0.5 THEN
E OUTPUT "Faulty reading"
Line D — A large difference from the trusted value signals a measurement error. The condition should be diff > 0.5. Using < flags readings that are actually close to correct.
Question 3
A scale ← 62.5
B actual ← 60.0
C error ← scale + actual
D OUTPUT "Error: ", error
Line C — The measurement error is the difference between the reading and the true value, so it should be scale - actual. Adding them gives a meaningless number.
Question 4
A birth_year ← 2009
B age ← 2025 + birth_year
C OUTPUT "Age: ", age
Line B — Age is found by subtracting the birth year from the current year, so it should be 2025 - birth_year. Adding gives an impossible age and the data would be inaccurate.
Question 5
A tolerance ← -0.5
B diff ← ABS(reading - actual)
C IF diff ≤ tolerance THEN
D OUTPUT "Accurate"
Line A — A tolerance is the allowed size of an error, so it cannot be negative. With -0.5, no reading could ever pass the accuracy check. It should be 0.5.

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