CodeHS Data-Driven Decision Making 3 — Questions and Answers
Question 1: Which data cleaning step addresses the problem of the same customer being listed as 'John Smith' and 'JOHN SMITH' in a dataset?
- Removing duplicates
- Handling missing values
- Standardizing formats (Correct answer)
- Removing outliers
Correct answer: Standardizing formats
Standardizing formats (e.g., converting all text to the same case) ensures consistent representation of the same entity.
Question 2: A bar chart showing app downloads per country is most useful for:
- Showing change over time
- Comparing values across categories (Correct answer)
- Displaying part-to-whole relationships
- Revealing correlation between two variables
Correct answer: Comparing values across categories
Bar charts excel at comparing discrete categories against a common quantitative axis.
Question 3: If a dataset has values 4, 8, 8, 10, 15, the MODE is:
- 8 (Correct answer)
- 9
- 10
- 15
Correct answer: 8
The mode is the value that appears most frequently; 8 appears twice while all other values appear once.
Question 4: A/B testing is BEST described as:
- Analyzing historical sales data to forecast revenue
- Comparing two versions of something to see which performs better (Correct answer)
- Cleaning a dataset before analysis
- Grouping similar customers into segments
Correct answer: Comparing two versions of something to see which performs better
A/B testing exposes two groups to different versions (A and B) and measures which produces the desired outcome.
Question 5: Which Python library is most commonly used for data manipulation and analysis using DataFrames?
- Matplotlib
- Pandas (Correct answer)
- Scikit-learn
- Flask
Correct answer: Pandas
Pandas provides the DataFrame structure and tools for loading, cleaning, and transforming tabular data.
Question 6: A data analyst finds that 5% of values in an important column are NULL. The BEST action depends on:
- The color scheme of the dashboard
- Whether the missing data is random or systematic, and how it affects the analysis (Correct answer)
- The number of columns in the table
- Whether the database uses SQL or NoSQL
Correct answer: Whether the missing data is random or systematic, and how it affects the analysis
The handling strategy (imputation, removal, flagging) depends on why data is missing and the impact on conclusions.
Question 7: In data storytelling, what is the primary purpose of an annotation on a chart?
- To increase the file size of the visualization
- To add color gradients to bars
- To highlight and explain a specific data point or trend for the audience (Correct answer)
- To change the chart type automatically
Correct answer: To highlight and explain a specific data point or trend for the audience
Annotations direct the viewer's attention to significant findings and provide context that the chart alone cannot convey.
CodeHS Data-Driven Decision Making 3
Which data cleaning step addresses the problem of the same customer being listed as 'John Smith' and 'JOHN SMITH' in a dataset?