DSE Knowledge 2 — Questions and Answers
Question 1: Which probability distribution is most appropriate for modeling the number of events occurring in a fixed time interval?
- Normal distribution
- Poisson distribution (Correct answer)
- Binomial distribution
- Exponential distribution
Correct answer: Poisson distribution
The Poisson distribution models the count of independent events occurring in a fixed interval of time or space.
Question 2: What does the term 'bias-variance tradeoff' describe in machine learning?
- The tradeoff between model accuracy on training vs. test data
- The tension between underfitting (high bias) and overfitting (high variance) (Correct answer)
- The balance between precision and recall metrics
- The relationship between feature count and training speed
Correct answer: The tension between underfitting (high bias) and overfitting (high variance)
Bias-variance tradeoff refers to the tension between a model's error due to oversimplification (bias) and its sensitivity to training data fluctuations (variance).
Question 3: In SQL, what does a LEFT JOIN return?
- Only rows that match in both tables
- All rows from the right table and matching rows from the left
- All rows from the left table and matching rows from the right (Correct answer)
- Only non-matching rows from both tables
Correct 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.
Question 4: What is the purpose of cross-validation in model evaluation?
- To speed up model training
- To estimate model performance on unseen data using multiple train/test splits (Correct answer)
- To reduce the number of features in a dataset
- To normalize input features to the same scale
Correct answer: To estimate model performance on unseen data using multiple train/test splits
Cross-validation repeatedly splits data into training and validation sets to produce a more reliable estimate of generalization performance.
Question 5: Which measure of central tendency is most resistant to outliers?
- Mean
- Mode
- Median (Correct answer)
- Weighted average
Correct answer: Median
The median is resistant to outliers because it depends only on the middle value(s), not the magnitude of extreme values.
Question 6: What does PCA (Principal Component Analysis) primarily accomplish?
- Classifies data into predefined categories
- Reduces dimensionality by projecting data onto directions of maximum variance (Correct answer)
- Clusters data points into groups
- Removes duplicate records from a dataset
Correct answer: Reduces dimensionality by projecting data onto directions of maximum variance
PCA transforms features into a smaller set of uncorrelated principal components that capture the most variance in the data.
Question 7: In the context of hypothesis testing, what does a p-value represent?
- The probability that the alternative hypothesis is true
- The probability of observing results at least as extreme as those seen, assuming the null hypothesis is true (Correct answer)
- The effect size of the observed difference
- The confidence level chosen by the researcher
Correct answer: The probability of observing results at least as extreme as those seen, assuming the null hypothesis is true
The p-value is the probability of obtaining a test statistic as extreme or more extreme than observed, under the assumption that the null hypothesis is true.
