DA Cheat Sheet 2026

The 30 highest-yield DA facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. What is the purpose of an index in a database? → Speed up data retrieval operations
2. Which statistical distribution is symmetric and bell-shaped? → Normal distribution
3. What does the pandas .fillna() method do? → Fills missing NaN values with a specified value or method
4. What does the pandas function df.describe() return? → Summary statistics (count, mean, std, min, max, percentiles) for numeric columns
5. Which SQL clause is used to filter rows after a GROUP BY operation? → HAVING
6. What is a confidence interval? → A range of values likely to contain the true population parameter
7. What is a primary key in a relational database? → A column that uniquely identifies each row
8. What is multicollinearity in regression analysis? → When two or more independent variables are highly correlated with each other
9. In Python, what does the NumPy function np.mean() calculate? → Arithmetic mean of array elements
10. What is the difference between revenue and profit? → Revenue is total income; profit is revenue minus costs
11. Which of the following is NOT a common type of chart used in data visualization? → Encryption chart
12. What does Customer Lifetime Value (CLV) measure? → The total revenue a business expects from a customer over their relationship
13. What is a leading indicator? → A forward-looking metric that predicts future outcomes
14. Which of the following is a sign of low-quality data? → High percentage of NULL values in critical fields
15. What is a data-driven decision? → A decision based on analysis of relevant data rather than intuition alone
16. What does YoY mean in financial reporting? → Year-over-Year — comparing a metric to the same period last year
17. What does ARPU stand for? → Average Revenue Per User
18. What is the primary purpose of a data governance framework? → To establish policies, standards, and accountability for managing data assets
19. In Excel, which function is used to look up a value in a table and return a corresponding value from another column? → VLOOKUP
20. What is the purpose of data profiling? → Assessing data quality, structure, and content before analysis
21. What Excel function counts cells that meet a specific condition? → COUNTIF
22. What is the interquartile range (IQR)? → The difference between Q3 and Q1
23. Which of the following is a best practice when designing a data report? → Keeping the report clear, concise, and focused on the main objectives
24. Which aggregate function counts only non-NULL values in a column? → COUNT(column_name)
25. Which algorithm is commonly used for classification tasks in data mining? → Decision tree
26. Which type of machine learning algorithm is commonly used for clustering? → K-Means
27. What is data normalization? → Scaling numeric values to a common range such as 0 to 1
28. What is the purpose of the SQL DISTINCT keyword? → Remove duplicate rows from the result set
29. What does a correlation coefficient of -0.9 indicate? → Strong negative relationship
30. What is the difference between structured and unstructured data? → Structured data fits in predefined rows/columns; unstructured data lacks a fixed schema