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Data Cleaning Techniques

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Data Cleaning Techniques

Choose the best answer where asked. For written questions, explain your reasoning clearly. Treat unusual values as clues to investigate, not automatic errors.

Recognising data issues

1.A class survey contains spelling differences, missing entries and repeated responses. What is the main purpose of cleaning this data?

To make the dataset ready for analysis by checking and addressing errors or inconsistencies
To remove every value that is different from the most common value
To change the results until they support a preferred conclusion
To replace all text entries with numbers

2.A school survey records a student's height as 164 cm in one row and 164 m in another. Which data-quality issue should be checked first?

A possible unit or entry error
A duplicate response
A missing value
A change in category labels

3.A dataset has a blank value in its 'minutes of exercise' column. Which is the most appropriate first step before deciding how to handle the blank?

Remove the affected row immediately
Estimate a value using a chosen method
Leave it blank and document what the blank means
Enter 0 automatically, even if the person may have exercised
Check the original survey record for the missing value

4.Match each data-cleaning term with its description.

Imputation
Recategorisation
Outlier
Duplicate record
Standardisation
Validation check

Combining different labels that represent the same group
A value far from most of the other values that may need checking
A rule used to flag values that may be invalid
Filling a missing entry using a chosen estimate
A response that has been recorded more than once
Putting entries into a consistent format or unit

Practising with a survey dataset

Response ID

Reading time (minutes)

Favourite genre

R01

Fantasy

R02

Sci-fi

R03

blank

Fantasy

R04

450

fantasy

R02

Sci-fi

5.Using the survey table, identify two entries that should be investigated or cleaned, and explain what seems wrong or inconsistent about each one.

6.The table contains two identical R02 responses. What is the likely cleaning action, and what should be checked before removing one?

7.A sports survey records weekly cycling distance as 8 km, 8000 m, 5 km and 5000 m. Rewrite all four values in kilometres, using one consistent format.

8.A money column contains the entries '$42,500', '42500' and '$42 500'. Describe one cleaning rule that would make these values consistent, and give the resulting format for all three.

9.A dataset has one missing test score. Explain when you might leave it blank rather than estimate it, and describe one way your choice could affect a later analysis.

10.When cleaning personal survey data, state one ethical step that can help protect the people who responded.