01. A team keeps its dataset at 2,000 records but expands each record from 10 features to 1,000 features.
Which two effects of the curse of dimensionality should the team expect?
(Choose two.)
a) The number of records needed to cover the feature space grows sharply
b) The model tends to underfit, since it has too few parameters to fit the data
c) The nearest and farthest neighbors of a record become almost equally distant
d) Each record moves closer to its nearest neighbor, sharpening distance-based methods
02. A lender's default model was trained before an economic downturn. Monitoring shows that applicants' incomes, debts and ages look much as they did in training, but applicants at the same income and debt levels now default far more often than before.
Which form of distribution shift does this describe?
a) Overfitting, because the model learned noise and quirks that do not hold in new data
b) Covariate shift, because the mix of incomes and debts has moved away from training
c) Selection bias, because training data left out applicants who later defaulted
d) Concept drift, because the relationship between inputs and outcome has changed
03. An analyst compares a new recommendation model with the current one on 20 different engagement metrics, testing each at the 0.05 significance level. One metric gives p = 0.04, and the analyst plans to report that the new model is better.
Which two steps reduce the risk that this result is a false positive?
(Choose two.)
a) Adding observations for that metric and retesting until it stays significant
b) Naming a single primary metric before the data is collected
c) Dividing the significance level by the number of tests performed
d) Repeating the tests with a significance level of 0.10 instead
04. A hospital team first builds a model that predicts each patient's length of stay in days. Managers then ask for a prediction of only whether a stay will be short (under 4 days) or long (4 days or more), and the team retrains the model on that two-value label.
Which statement BEST describes the effect of this change?
a) The task becomes classification, because the model now predicts one of two categories
b) The task becomes clustering, since the patients now fall into two groups
c) The task becomes classification, and the model can learn it without labeled examples
d) The task stays regression, because its labels are still derived from a count of days
05. A team estimates the mean daily error of its demand-forecasting model. It draws 1,000 bootstrap resamples of the observed errors and computes the mean of each. Sorted from smallest to largest, the 25th bootstrap mean is 4.1, the 50th is 4.3, the 500th is 5.0, the 950th is 5.9 and the 975th is 6.2.
What is the 95% percentile bootstrap confidence interval for the mean error?
a) 4.3 to 5.9, from the 5th and 95th percentiles
b) 4.1 to 5.0, from the 2.5th percentile and median
c) 5.0 to 6.2, from the median and the 97.5th percentile
d) 4.1 to 6.2, from the 2.5th and 97.5th percentiles
06. A startup has only 300 labeled records for a churn model. Each time it reshuffles the data and makes a new 80/20 train-test split, the test accuracy shifts by several points.
Why would 5-fold cross-validation give a more trustworthy estimate here?
a) It scores the training folds as well as the test fold, so each result draws on all 300 records
b) It averages five scores in which every record is tested once, so one lucky split matters less
c) It creates new synthetic records for each fold, so the small dataset becomes much larger overall
d) It trains on all 300 records together, so that none of the data has to be held back for testing
07. Two analysts at an insurance firm each retrain a claims model on what they believe is the same curated dataset and get noticeably different accuracy. They discover that someone corrected several thousand labels last month and left no record of the change.
Which curation practice would have prevented this confusion?
a) Versioning the dataset and logging each change along with its reason
b) Converting the dataset from CSV to JSON so each record describes itself
c) Fixing the random seed used when the model is initialized and trained
d) Collecting additional claims records so small edits matter less
08. A hospital deploys a model that predicts patient no-shows for appointments. Actual attendance is confirmed only days later, and the team wants to know when production data drifts away from the training data.
Which two monitoring practices help detect data distribution shift?
(Choose two.)
a) Re-scoring the original held-out test set every week and checking its accuracy
b) Monitoring how long the model takes to return each prediction to the scheduler
c) Comparing the distribution of each live input feature with its training distribution
d) Tracking accuracy on recent production cases once their outcomes are confirmed
09. A team compares bagging and boosting on a dataset of product reviews in which about 15% of the sentiment labels are known to be wrong. Boosting's test accuracy drops as more rounds are added, while bagging's stays steady.
What BEST explains boosting's behavior?
a) Each round averages independent models, so it mainly lowers variance as bagging does
b) Each round weights misclassified records more, so mislabeled reviews gain focus
c) Each round drops the hardest records, so the model loses the reviews it most needs
d) Each round trains on a fresh bootstrap sample, so the mislabeled reviews are averaged away
10. A retailer runs k-means with k = 5 on its customer purchase data. Each run starts from randomly chosen centroids, and some runs produce segments that are clearly worse than others. The analyst wants the result LEAST likely to be a poor local solution.
Which two practices address this?
(Choose two.)
a) Choose initial centroids spread far apart from one another, as the k-means++ method does
b) Raise k after every run until two runs in a row return the same segments
c) Place all five initial centroids close together near the densest region of the data
d) Run it several times from different random starts and keep the lowest within-cluster distance