Facebook Data Scientist Mock Interview - Segment Influencers

Isn' the Beta of the logistic regression the change in Y (or log odds in this case) given a 1 unit change in X?

If so, then it is possible for Beta to be 0 (or 0 to be in beta's confidence interval) as that implies a 1 unit change in x does not have any change in log odds. However, if we want to look at odds, then we need to take the exponential of Beta, in which case it is not possible for the confidence interval of exponential of Beta to contain 0.

The confidence interval here is not referring to the log odds, but the change in log odds given a change in x.

The first question, Do we really need a maximum likelihood estimate to deal with getting beta coefficients for regression problem? I think it will only been used in classification, right? Will gradient descent be the correct answer?

Hi, I also want to give my mock interview.
Could you take it please?
I am doing my graduation and currently, I am in 3rd year of computer science.
I want to be good in data science

WTF? I didn't know they would go so deep into statistics. Multivariate regression? Derive the Beta coefficient? Wow, I'm stumped right at the beginning. :(

Um, the expression for beta is wrong (first question). its -
beta = (X'X)^(-1)X'Y

Thank god it wasn't expected to derrive the MLE. Also, I am a bit surprised FB expects someone to remember the OLS matrix equations for beta coefficients. I mean, it was lasered into my brain sure, but I am not sure that's proof of anything other than I happened to commit it to memory. I also happened to commit the equations for generalized method of moments, but that's also not proof of anything.

Watching her struggle with a simple SQL question really made me feel better

Sql#1: Correct MYSQL query is:
select user_name, ROW_NUMBER() over () as 'Rank'
from Messages
window w as (partition by date order by message_sent/message_received desc)

Dang coefficient would've gotten me off the bat. Idda said run regression and print the summary...whoops.

done

amazing, super helpful!

Actually the confidence interval is not interpreted as the chance that true value falls in the interval but the accurate interpretation should be there is 95% probability that the random interval falls on the true value.

Like the stat questions

That is not the confidence interval, that is credible interval. Confidence interval means 95 % of the time the estimated beta coefficient will predicted the correct result which “y”.
To get 95 % confidence of beta coefficient we need to use Bayes parameter estimation which will give you a posterior distribution of beta coefficient with 95% credible interval.

I don't think she answered the question right on the log odds correctly. CI in log odds is insignificant if it includes 0. CI for odds is insignificant for including 1

SQL Q1: should not the window function be rank() instead of row_number()? It is possible to have multiple users who get the identical highest ratio for a given day.

Thanks a lot for sharing? May I ask which level this mock interview is meant for?

What was the experience in years for interviewer & interviewee ?

That function in JavaScript is annoying me, please use ES6 arrow function for binding.

The case study probably want to follow this structure: 1. why you want to distinguish influencer account ? [let's see it's for better target ads, or use these informations in recommender system, etc] 2. What kind of data are available to us (account contextual information and behavioral information)? 3. Clarify which features that can be helpful (can talk about some classification models here, but mainly should be features insights) 4. clarify which features are most important (from product sense and machine learning points- e.g. permutation importance, gini importance) 5. Summarize it.

Lol these questions are a joke. I broke into fb. Least squires, MLE or gradient descent. Ans:
Logistic regression, or something classsifier.
Confidence intervals-these are estimates of regression variables.
Presence of 0, u have to do t-test on the individual variable

Anyone want to come and join a group of mock interview for data analyst? I'm looking for people to mock together, in aspects of coding, behavioral questions, and resume. Thanks!

Interview was fine. Its a mock for a reason, and they all tend to differ here and there. Practicing is better than not practicing at all!

The case study has been worked in detail. An additional important feature could be if there any other influencers following the particular user under consideration

solution for 1st SQL Question:
select
t_date,
user_name
from messages
where message_received != 0
group by t_date, user_name
order by sum(message_sent)::float/sum(message_received) desc
limit 1;

Hi - was a Facebook DS and I gave many interviews. This is nothing like the Facebook DS interview.

Hardly see anything...dark and font too small

I feel like this is not the typical fb style interview, but I definitely learned something useful here!

I’m going with a reverse engineering path into college, please tell me I don’t have to learn these things.

... a friend of mine was asked to write an algorithm for search autofill during the case portion of their interview

The third question about the confidence interval of logistic regression is kind of misleading and challenge from the interviewee's perspective. More clarification work should help to understand like if it is the logit format or probability format. First, the question is asking if log-odds (logit) could be 0, I think it is possible, log(p/1-p) definitely could be zero when p=1-p, then you jumped to the confidence interval of the odds ratio, which is kind of tricky if you are treating the odds ratio and log odds as the same stuff (odds ratio is not taking log). The odds ratio format should be like the exp(beta), then when 1 included in the CI, that means beta could be zero since exp(0)=1, then accept the null hp to say beta coefficient is not significant.

The first sql you have to create a subquery, or use HAVING instead of WHERE.

The first sql answer is incorrect you cant filter on rank yet, you have to create a sub query.

Thanks for such an insightful content!

I have a clarification question on 3rd stat problem. You asked if log-odds i.e. logit value can be 0 or not. Since the logit scale is -infinity to +infinity, log-odds can have 0 values dont they? She answered cannot have 0 but minimum of 1.

I would appreciate if you can clarify if that was the right answer or I am missing something here. Thanks again! 👍

Hello, I don't know why people are being so cold, you did great on the interview.

For the influencer versus non-influencers, could you do something where first you identify those who actually have content that has products that are being 'advertised', then you correlate the presence/views of that video with sales of that product. If correlation reaches above a certain point then they are an influencer.

Cant see anything to small. Zoom in

Where do I start if I want to learn the skills needed to go into data science? I just started a statistics class and Ive been really interested in the modeling and practical applications. I only barely understand the basics of R and SQL to give you an idea of where my knowledge is. Thanks for the video

I read the title A Facebook data scientist mocks interviews

Thank you for the video. Pretty informative.

This shows imposter syndrome is real.

I do understand that there were follow-up interviews and further rounds, but it does give much more confidence, given that it is a SENIOR interview at FACEBOOK.

I am now actually considering to try out Data Scientist path some time in the future.

This is the sort of stuff we covered on the Msc Data Science course in the UK, I cant believe its a senior level interview

I have never been asked these type of statistics questions or to derive formulas or coefficients on a data science interview.

Is that a junior level interview?

Hey the font size is too small, can you please post the questions somewhere?

her keyboard I imagine made of keys made of ten inch springs with wooden top :D

It would be helpful to post the correct answers at some point in the future