DA0-002 Data Analysis Practice Test 7 — 15 Questions

Question 1

A data analyst runs an A/B test on a new website layout. The test yields a p-value of 0.04 with the null hypothesis being no difference in conversion rates. The significance threshold is α=0.05. Which of the following is the correct conclusion?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Reject the null hypothesis; there is a statistically significant difference in conversion rates.. Since p-value (0.04) < α (0.05), we reject the null hypothesis and conclude there is a statistically significant difference. However, statistical significance does not guarantee practical significance.

Answer

The result is not significant; accept the alternative hypothesis.

Answer

Reject the null hypothesis; the new layout is proven to increase conversions.

Answer

Fail to reject the null hypothesis; there is no evidence of a difference.

Question 2

A dataset contains a column 'Age' with values: [22, 25, 25, 30, 35, 40, 45]. What is the interquartile range (IQR)?

Accepted Answer

15. Q1 is median of lower half (22,25,25) = 25; Q3 is median of upper half (35,40,45) = 40; IQR = 40-25 = 15.

Answer

10

Answer

20

Answer

25

Question 3

A data analyst wants to understand the relationship between advertising spend and sales revenue. The analyst calculates a Pearson correlation coefficient of 0.85. Which of the following is the best interpretation?

Accepted Answer

There is a strong positive linear relationship between advertising spend and sales.. Pearson r ranges from -1 to +1; 0.85 indicates a strong positive linear relationship, but correlation does not imply causation.

Answer

85% of the variation in sales is explained by advertising spend.

Answer

Increasing advertising spend by $1 will increase sales by $0.85.

Answer

There is a strong negative linear relationship between advertising spend and sales.

Question 4

In a logistic regression model predicting customer churn (1 = churn, 0 = not churn), the coefficient for 'contract length' is -0.5. Which of the following is the correct interpretation?

Accepted Answer

For each unit increase in contract length, the log-odds of churn decrease by 0.5.. In logistic regression, coefficients represent the log-odds change. A negative coefficient decreases the log-odds, meaning lower probability of churn.

Answer

Longer contract length increases the odds of churn.

Answer

The probability of churn decreases by 50% for each unit increase in contract length.

Answer

Contract length is not a significant predictor.

Question 5

A data analyst is cleaning a dataset and finds that 5% of values in the 'income' column are missing. The analyst decides to impute missing values using the mean of the non-missing values. Which potential issue should the analyst be most concerned about?

Accepted Answer

The imputation may reduce the variance and distort the distribution.. Mean imputation reduces variance and can distort relationships, especially if data is skewed. It may also bias estimates if missingness is not random.

Answer

The imputation is not valid because the missing rate is too low.

Answer

The imputation will increase the standard deviation of the variable.

Answer

The imputation will create outliers.

Question 6

A data analyst wants to use a Z-score to standardize a dataset. The variable has a mean of 50 and a standard deviation of 10. What is the Z-score for a raw value of 70?

Accepted Answer

2. Z = (X - mean) / std = (70 - 50) / 10 = 2.

Answer

0.5

Answer

20

Answer

-2

Question 7

A data scientist is using K-means clustering with k=3. After the first iteration, the centroids are recalculated. Which step occurs next in the algorithm?

Accepted Answer

Assign each point to the nearest centroid. In K-means, after recalculating centroids, each point is reassigned to the nearest centroid, then centroids are updated again, iterating until convergence.

Answer

Calculate the sum of squared errors

Answer

Stop the algorithm because k is fixed

Answer

Compute the elbow curve

Question 8

A data analyst is evaluating data quality for a customer database. Which TWO dimensions of data quality are most directly affected by duplicate customer records?

Accepted Answer

Accuracy. Duplicates reduce accuracy (records may be incorrect) and uniqueness (each entity should appear once).

Answer

Consistency

Answer

Timeliness

Answer

Completeness

Question 9

A data analyst is performing a chi-square test of independence on a contingency table of customer satisfaction (satisfied, neutral, dissatisfied) by region (North, South, East, West). Which THREE of the following are necessary assumptions for the test?

Accepted Answer

The two variables are categorical. Chi-square test requires categorical variables, expected frequencies >=5 in at least 80% of cells, and independence of observations.

Answer

The sample size is greater than 30

Answer

The data must be normally distributed

Question 10

A data analyst is preparing to run an A/B test comparing two email subject lines. Which TWO of the following should the analyst define before the test begins?

Accepted Answer

The null and alternative hypotheses. Before A/B testing, define null and alternative hypotheses, and determine sample size needed for desired statistical power and effect size.

Answer

The exact lift in conversion rate

Answer

The time series decomposition

Answer

The p-value after the test

Question 11

A data analyst calculates the mean, median, and mode of a dataset. Which of the following measures of central tendency is least affected by extreme outliers?

Accepted Answer

Median. The median is resistant to outliers because it is the middle value, whereas the mean is pulled by extreme values and the mode may not be affected but is less robust for continuous data.

Answer

Range

Answer

Mode

Answer

Mean

Question 12

A data analyst is conducting an A/B test on a website's landing page. The null hypothesis is that there is no difference in conversion rates between the control and treatment groups. After collecting data, the analyst calculates a p-value of 0.03. Using a significance level of α = 0.05, what is the correct conclusion?

Accepted Answer

Reject the null hypothesis; the treatment group has a higher conversion rate.. Since p < α, the null hypothesis is rejected, indicating a statistically significant difference in conversion rates.

Answer

Accept the null hypothesis; the difference is due to chance.

Answer

Fail to reject the null hypothesis; there is no evidence of a difference.

Answer

The result is inconclusive because the p-value is close to 0.05.

Question 13

A data scientist is analyzing a dataset with multiple features and wants to apply k-means clustering to segment customers. She chooses k = 4 based on the elbow method. During the iteration process, which of the following correctly describes a step in the k-means algorithm?

Accepted Answer

Assign each point to the nearest centroid based on Euclidean distance, then update centroids as the mean of points in each cluster.. K-means iteratively assigns each point to the nearest centroid, then recalculates centroids as the mean of points in the cluster.

Answer

Compute the covariance matrix and use principal components to initialize centroids.

Answer

Use hierarchical clustering to determine initial centroids.

Answer

Randomly assign centroids and then compute distances to the cluster medians.

Question 14

An analyst is performing a linear regression and obtains an R-squared value of 0.85. Which of the following is the best interpretation?

Accepted Answer

The model explains 85% of the variability in the dependent variable.. R-squared indicates the proportion of variance in the dependent variable explained by the independent variable(s). 0.85 means 85% explained.

Answer

85% of the residuals are zero.

Answer

85% of the data points lie on the regression line.

Answer

There is an 85% chance that the relationship is causal.

Question 15

A dataset contains the ages of 100 customers. The analyst wants to transform the ages to a 0-1 range for use in a distance-based algorithm. Which technique should be used?

Accepted Answer

Min-max normalization. Min-max normalization scales features to a fixed range, typically 0-1.

Answer

Square root transformation

Answer

Log transformation

Answer

Z-score normalization