DA0-002 Data Analysis Practice Test 14 — 15 Questions

Question 1

Which data quality dimension ensures that data represents the real-world scenario correctly and without errors?

Accepted Answer

Accuracy. Accuracy means the data correctly reflects reality.

Answer

Completeness

Answer

Consistency

Answer

Timeliness

Question 2

A financial analyst wants to compare the mean annual returns of three different investment strategies. Which statistical test is most appropriate?

Accepted Answer

One-way ANOVA. ANOVA is used to compare means of three or more groups.

Answer

Chi-square test

Answer

Paired t-test

Answer

Two-sample t-test

Question 3

In logistic regression, the output is a probability between 0 and 1. If the predicted probability for a customer churning is 0.7 and the decision threshold is 0.5, what is the predicted class?

Accepted Answer

Churn (class 1). Since 0.7 > 0.5, the predicted class is churn (usually coded as 1).

Answer

Not churn (class 0)

Answer

Both classes equally likely

Answer

Uncertain, need more data

Question 4

A data analyst is cleaning a dataset and finds that the 'age' column has several missing values. Which method of handling missing values is least likely to introduce bias if the missingness is completely at random?

Accepted Answer

Listwise deletion. Listwise deletion (removing rows with missing values) is simple and unbiased if data is MCAR, but it reduces sample size. However, it is least likely to introduce bias among the options when MCAR holds.

Answer

Mean imputation

Answer

Mode imputation

Answer

Forward-fill

Question 5

A data scientist applies K-means clustering to a customer dataset. The elbow method suggests using 4 clusters. After running K-means with k=4, the within-cluster sum of squares (WCSS) is plotted against k, and the elbow is at k=4. What does this indicate?

Accepted Answer

Increasing k beyond 4 would not significantly reduce WCSS.. The elbow method suggests that increasing k beyond 4 yields diminishing returns in reducing WCSS; k=4 is a good trade-off.

Answer

The data naturally forms 4 clusters with no noise.

Answer

The algorithm converged to a local minimum.

Answer

The model has overfit the data.

Question 6

A retail company wants to identify customer segments based on purchase history and demographics. Which technique is most appropriate for this task?

Accepted Answer

K-means clustering. K-means clustering is an unsupervised learning technique designed to segment data into groups based on similarity.

Answer

Linear regression

Answer

Chi-square test

Answer

Logistic regression

Question 7

An analyst is preparing data for a clustering algorithm that uses Euclidean distance. Which TWO data preprocessing techniques should be applied to ensure all features contribute equally?

Accepted Answer

Min-max normalization. Min-max normalization and Z-score standardization both scale features to comparable ranges, preventing features with larger scales from dominating distance calculations.

Answer

Log transformation

Answer

Principal component analysis

Answer

One-hot encoding

Question 8

A data analyst is evaluating the quality of a customer database. Which THREE of the following are dimensions of data quality?

Accepted Answer

Completeness. Accuracy, completeness, and timeliness are standard data quality dimensions.

Answer

Correlation

Answer

Variance

Question 9

A researcher is designing an A/B test to compare two website layouts. Which TWO elements are essential for determining the required sample size?

Accepted Answer

Statistical power. Statistical power and desired effect size are key inputs for sample size calculation.

Answer

Sample mean

Answer

Confidence interval width

Answer

P-value

Question 10

A data analyst is examining the distribution of customer ages in a dataset. The ages are: 22, 25, 29, 30, 31, 34, 35, 37, 40, 42, 45, 50, 55, 60, 65. Which measure of central tendency would be least affected by an outlier if a value of 120 is incorrectly recorded as age 120?

Accepted Answer

Median. The median is resistant to outliers because it is the middle value when data are sorted. The mean is sensitive to extreme values, and the mode may not change but is not a robust measure of central tendency. The range is a measure of spread, not central tendency.

Answer

Mode

Answer

Mean

Answer

Range

Question 11

A company wants to determine if there is a significant difference in the average sales revenue between two different store layouts. They collect sales data from 30 stores with Layout A and 30 stores with Layout B. Which statistical test is most appropriate for comparing the means of these two independent groups?

Accepted Answer

Two-sample t-test. The two-sample t-test (independent t-test) compares the means of two independent groups. A paired t-test would be for dependent samples, ANOVA for three or more groups, and chi-square for categorical variables.

Answer

ANOVA

Answer

Chi-square test

Answer

Paired t-test

Question 12

In a regression analysis, the coefficient of determination (R²) is 0.85. How should this value be interpreted?

Accepted Answer

85% of the variance in the dependent variable is explained by the model. R² represents the proportion of variance in the dependent variable that is explained by the independent variable(s). An R² of 0.85 means the model explains 85% of the variability.

Answer

85% of the data points lie on the regression line

Answer

The slope of the regression line is 0.85

Answer

85% of the independent variables are significant

Question 13

A data scientist is building a K-means clustering model for customer segmentation. After plotting the within-cluster sum of squares (WCSS) against the number of clusters (k), she observes that the WCSS decreases sharply until k=5 and then levels off. Which value of k should she choose based on the elbow method?

Accepted Answer

k=5. The elbow method suggests selecting the number of clusters at the point where the WCSS starts to diminish less rapidly, forming an 'elbow'. Here, the elbow is at k=5, where adding more clusters yields diminishing returns.

Answer

k=6

Answer

k=4

Answer

k=3

Question 14

A stock analyst is analyzing monthly sales data for a retail company and observes a consistent pattern of high sales every December. This pattern is most likely an example of which time series component?

Accepted Answer

Seasonality. Seasonality refers to regular, predictable patterns that repeat at fixed intervals (e.g., yearly, monthly). The consistent December peak indicates a seasonal pattern.

Answer

Irregular

Answer

Cyclical

Answer

Trend

Question 15

In an A/B test, the null hypothesis states that there is no difference between the conversion rates of the control and treatment groups. After collecting data, the p-value is 0.03. Using a significance level α = 0.05, what should the analyst conclude?

Accepted Answer

Reject the null hypothesis; there is a significant difference. Since the p-value (0.03) is less than α (0.05), the null hypothesis is rejected, indicating a statistically significant difference between the groups.

Answer

Accept the alternative hypothesis; the treatment is better

Answer

The test is inconclusive

Answer

Fail to reject the null hypothesis; no significant difference