Data Science Online Test

The following .csv file contains the data from a classifier model that predicts if an image contains a dog: predictions.csv 

The first column contains information if the dog is in the image or not. The second column contains the classifier prediction, which is in the interval 0-100, with higher values meaning that the classifier is more confident that image contains a dog.

What is the value of the decision boundary that will maximize the accuracy of the model? Values greater than or equal to the decision boundary will be treated as positive.

Each day during 2019 an agency asked a hundred randomly selected people which party they would vote for if elections were held that day. Results of the poll were recorded in the following file. The Workers' Party asked for the report which they plan to use to improve their strategy for upcoming elections.

Fill in the missing values in the report for 2019:

• The arithmetic mean of votes for the Workers' Party is: __ (rounded to one decimal place)
• The median of votes for the Workers' party is: __ (rounded to closest integer)
• The standard deviation of votes for the Workers' party is: __ (rounded to one decimal place)
• The difference between the largest and the smallest number of votes for the Workers' party for March is: __
• The largest number of votes that any party received on any day is: __ votes.
  That maximum was achieved on 2019-__-__ by __.
• The party with the largest difference between the maximum and minimum number of votes is _______. That difference is __ votes.

Two bacteria cultures, A and B, were set up in two different dishes, each covering 50% of its dish. Over 20 days, bacteria A's percentage of coverage increased to 70% and bacteria B's percentage of coverage reduced to 40%:

The marketing team of the telecommunications company launched an SMS campaign to encourage customers to make more countrywide calls. The manager of the team asked you to analyze the results of the campaign.  Your main goal is to predict which customers are most likely to increase their number of calls as a result of similar SMS campaigns in the future. You have created a Random Forest model but it has problems with fitting the actual training dataset.

Which of the following steps can be taken to reduce underfitting and improve the model’s performance?

Your company is running a test that is designed to compare two different versions of the company’s website.

Version A of the website is shown to 60% of users, while version B of the website is shown to the remaining 40%. The test shows that 8% of users who are presented with version A sign up for the company’s services, as compared to 4% of users who are presented with version B.

If a user signs up for the company’s services, what is the probability that she/he was presented with version A of the website?

A SAAS company reported a 20% churn rate (the rate at which customers stop subscribing to a service ) in the last quarter, which is much larger than the expected 12%. Your manager asked you to create a model that can predict the churners of the next 12 months in advance. With the help of this model, the marketing team will launch churn prevention campaigns to reduce the churn rate.

You decided to use a Gradient Boosting model. The parameters used in the model are the following:

• Learning rate = 0.3
• Maximum depth of a tree = 6
• Minimum sum of instance weight needed in a child = 1
• Subsample = 1
• L1 regularization term on weights = 0
• L2 regularization term on weights = 1

Currently the model has a problem, the training set has more than 95% accuracy but the test set has only 60% accuracy.

Which of the following steps can help solve the issue?

A classifier that predicts if an image contains only a cat, a dog, or a llama produced the following confusion matrix:

What is the accuracy of the model, in percentages?