Mixed Deck — All DA Topics Flashcards
100 cards from real DA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 20 Mixed Deck — All DA Topics flashcards as text
Which test is appropriate for comparing proportions between two independent groups?
Answer: Chi-square test
The chi-square test of independence is used to determine if there is a significant association between two categorical variables or proportions.
What does the SQL ORDER BY clause do?
Answer: Sorts result rows by one or more columns
ORDER BY sorts query results in ascending (ASC, default) or descending (DESC) order based on specified columns.
Which SQL clause limits the number of rows returned by a query?
Answer: All of the above (syntax varies by database)
Different databases use different syntax: LIMIT (MySQL/PostgreSQL), TOP (SQL Server), or ROWNUM (Oracle) to restrict the number of returned rows.
What is the primary goal of data mining?
Answer: To extract useful patterns and knowledge from large datasets
The primary goal of data mining is to extract useful patterns, insights, and knowledge from large datasets. It involves using various techniques to discover hidden relationships and trends that might not be immediately obvious. This knowledge can then be used for decision-making, prediction, and understanding complex systems.
What is one-hot encoding used for in data preparation?
Answer: Converting categorical variables into binary numeric columns
One-hot encoding transforms each category level into a separate binary column (0 or 1), enabling algorithms that require numeric input to process categorical data.
What is a subquery in SQL?
Answer: A query nested inside another query
A subquery is a query embedded within another SQL query, often in the WHERE, FROM, or SELECT clause.
What is a left join imputation strategy?
Answer: Filling NULLs from a reference lookup table via a left join
Joining a dataset to a reference table on a key and using matched values to fill NULLs is a practical imputation strategy in SQL-based data preparation.
What does 'vectorization' mean in the context of pandas or NumPy?
Answer: Applying operations to entire arrays without explicit Python loops
Vectorization applies operations element-wise across arrays using optimized C-level code, making computations significantly faster than Python loops.
Which of the following is a best practice when designing a data report?
Answer: Keeping the report clear, concise, and focused on the main objectives
When designing a data report, it is a best practice to prioritize clarity, conciseness, and focus on the main objectives. This ensures that the audience can easily understand the key messages and insights without being overwhelmed by unnecessary detail or jargon. A clear and focused report helps stakeholders quickly grasp the findings and make informed decisions.
Which of the following best describes an outlier?
Answer: A value significantly different from the rest of the dataset
An outlier is a data point that lies far outside the typical range of values and can skew analysis results.
What does a LEFT JOIN return?
Answer: All rows from the left table and matching rows from the right
A LEFT JOIN returns all rows from the left table and the matched rows from the right table; unmatched right-table rows appear as NULL.
What is a cohort analysis?
Answer: Tracking behavior of groups sharing a common characteristic over time
Cohort analysis groups users by a shared attribute (e.g., sign-up month) and tracks their behavior over time to reveal retention and engagement patterns.
What does the COALESCE function do in SQL?
Answer: Returns the first non-NULL value in a list
COALESCE evaluates its arguments in order and returns the first non-NULL value, making it useful for handling missing data.
What is a CTE (Common Table Expression) in SQL?
Answer: A temporary named result set defined within a WITH clause
A CTE is a temporary, named result set created with the WITH keyword that can be referenced within the same query.
Which statistical distribution is symmetric and bell-shaped?
Answer: Normal distribution
The normal distribution is symmetric around its mean and produces the familiar bell-shaped curve.
What is the primary goal of machine learning?
Answer: To make predictions or decisions without being explicitly programmed
The primary goal of machine learning is to enable computer systems to learn from data and make predictions or decisions without being explicitly programmed for every scenario. Instead of following fixed instructions, ML algorithms build models based on training data, allowing them to identify patterns and adapt their behavior. This capability is fundamental to developing intelligent systems that can automate complex tasks and derive insights.
What does ARPU stand for?
Answer: Average Revenue Per User
ARPU (Average Revenue Per User) measures how much revenue a business earns on average from each user over a given period.
In a box plot, what does the line inside the box represent?
Answer: Median
The line inside the box of a box plot marks the median (Q2), the middle value of the dataset.
What does the pandas .drop_duplicates() method do?
Answer: Removes rows that are exact duplicates of other rows
drop_duplicates() removes rows where all (or specified) column values are identical to a previous row, keeping only unique records.
What is the main goal of differential privacy?
Answer: To add mathematical noise to datasets so individual records cannot be identified while preserving statistical utility
Differential privacy adds carefully calibrated statistical noise to query results so that no individual's data can be inferred, while aggregate insights remain valid.