ฝึกพูดภาษาอังกฤษด้วยเทคนิค Shadowing จากวิดีโอ: Learn how to SOLVE a data analytics case study problem

and then we ask the interviewer hey is that good

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and then we ask the interviewer hey is that good

or not

and they're like no do something a little bit more complicated

hi everyone today i'm going to solve a data analytics case

study problem first we're going to go over what constitutes a

data analytics problem a framework for how to tackle it

and then a step-by-step explanation of diving into it

so first off what is a data analytics case study for our purposes i've defined data analytics case study problems

as any problem that requires 1 formulating metrics for a hypothetical scenario

and 2 writing a SQL query or analyzing a dataset in Python to retrieve those metrics.

For example,

the problem we're tackling today involves understanding how to build a

new audio chat feature to improve the match rate between car buyers and sellers in a marketplace app.

Now if you're thinking that data analytics case study questions sound very similar to product metrics type questions,

you're probably right.

And for all intents and purposes,

most product metrics questions fall under the umbrella of data analytics.

It's just that product metrics questions are more focused around product case studies.

So for example, it'd be something like,

how would you investigate a 10% drop in Uber ride requests, right?

Or let's say that we want to launch a new feature for Uber,

how would you analyze results?

So all those product metrics questions are focused around a specific product itself

and so data analytics can be a little bit more broad than

that the second main difference is

that data analytics case studies questions we actually expect the candidate to use sql

or python to actually implement their metrics whereas in product metrics

case study questions you're usually just kind of brainstorming different ideas

clarifying the question giving out structured analysis without actually diving into the data itself

because there is no data it's a hypothetical scenario

so data analytics case studies what you'll find is

that they'll actually give you an actual data set many times this will happen in a take-home assignment

or an official phone screen

or even on an on-site where the interviewer will basically just give you a data set

and a python jupiter notebook and be like go to hand it's kind of nice

because basically it kills two birds with one stone

if you're an interviewer they're trying to assess how you do on sequel

and the same time they can also get a sense of your product intuition

The main issue with these is that if you have bad product intuition and you then work on a SQL query,

you're either going to make your life really difficult by working on a SQL problem that's extremely difficult

or on the entirely wrong problem.

So let's just dive into this question and then see how it goes.

All right.

An online marketplace company has introduced a new feature

that allows potential buyers and sellers to conduct audio chats with each other prior to transacting.

Let's say we have two tables that represents this data.

So we have a chats table and we have a marketplaces purchases table.

How would you measure the success of this new feature?

Write a query that can represent if this feature is successful or not.

How do we tackle this problem?

So the first thing we have to do is to treat this like it's a classic product metrics,

just any kind of analytics case study, right?

So we're doing stuff like we're clarifying,

we're assessing requirements, requirements, we're validating our solution.

Before that, we're proposing a solution and then we're validating it.

Yeah, let's just start out with that first.

And, you know, given the time constraints of most of these interviews,

I would say the most optimal thing

that we're going to be doing is actually be proposing one metric and immediately coding that up.

I think in every instance,

we also want to keep this metric pretty simple.

I see a lot of candidates shoot themselves in the foot by first proposing like a really complicated metric

and then

when they actually have to code it up in SQL they're

just spending you know like 40 minutes the rest of the time trying to get to a solution.

The best way and I think always the best way to approach this is always iteration right

so we iterate on our approaches we propose a simple solution

and then we code it up and we do that

and we do that fast and then we ask the interviewer hey is

that good or not and they're like no do something a little bit more complicated

and then they'll be like okay yeah so i'll do something new now

so again let's try to iterate on all of our solutions here

and start out by keeping it simple kiss framework right keep

it simple stupid the second tip is to keep the metric super flexible for further analysis okay

so if we start out with just one simple solution then we can actually make it flexible

so that later down the line

we are also not cheating ourselves on the foot again by having to rewrite our entire SQL query.

We want to be able to make it so

that we can actually write it in a way that is flexible for further solutions down the line.

Given this problem and given

that we have to understand how a feature basically allows users to conduct audio chats with each other,

try this again is just to visualize exactly what the output is that I want.

So I want something that says use audio chat,

right and then if it is a one or a zero then i want also purchase completion rates

and then this is going to be something like you know 50 and then this will be something like

25 right so this is the output that i want to see right

if i'm a pm i want to see that oh people

that use the audio chat completed their purchases at a higher rate than people

that did not use audio chat okay

so awesome we visualize this output we come up with this

metric this thing i want to note in our analysis is

that you know

if we'd like to expand the analysis we can actually analyze it by the call duration

or the number of calls and so uh conversations

that probably have on average three audio chats

or 2x the total length of call time then other conversations are more likely to have transactions completed than something

that has you know on average one audio chat

and then like 30 seconds of call time instead of one minute of call time on average

and those have a lower transaction rate let's say we're analyzing

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call chat time basically like 30 seconds 60 seconds 90 seconds

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and then we look at our metric that we care about which is purchase

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completion rates 30 percent 50 percent 69 basically we're seeing

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that you know on average if we bucket our call chat time

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and as the chat time goes longer the purchase completion rates

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go higher then probably this audio feature is then working for us

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so i just want to say that out of all of our metrics

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that we put together one thing

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that we do have to keep in mind is normalizing the data

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so usually we have to compare two equally interested groups of conversational buyers

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so that we know

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that the audio chat feature is actually making the difference it's not the fact

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that because i make more calls i'm already inherently more likely to complete a transaction

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and so a lot of that normalization you know we can't really do

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that with our existing data set so i would just make

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that assumption up front so that you get extra brownie points with your interviewer

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and you know most of the analytics problems are all causal inference

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if you mention you know you know causal inference they're like

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oh cool you know what causal inference is let me check off this box right to be honest

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that is really what a lot of interviewers and interviews are like

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because of the fact that they have to do

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so many interviews they're just trying to speed it up so they can get to their lunch break

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all right so let's just solve for this uh simple calculation first right we just want to know

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if they use the audio chat did they actually increase their

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purchase completion rate first i'm gonna write select from

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chats left join marketplace purchases as c as

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mp on c dot buyer user id equals mp.buyer user id look at

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that autocomplete oh my god we need to pay our engineers more

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user id is equal to mp.seller user id uh group by call connected

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so when we group by the call connected uh

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so as you can see we're doing double join right we

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want to join the buyer to the buyer of the chat

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and to the buyer of the marketplace we want to join

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the seller of the chat to the the seller of the marketplace.

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Then we want to group by if the call was connected or not.

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And then we want to grab the distinct marketplace ID divided by the distinct number of chats.

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And then I can just run this query.

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Hopefully it'll run.

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I have an error.

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Of course, I have an error.

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I didn't comment this out.

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Let me comment this out.

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Cool.

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Awesome.

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So as you can see below,

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and I'll with my video.

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The number of calls that were connected resulted in a higher conversion rate.

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Obviously, this is fake data,

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so of course it was going to.

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So we're good, except I spot an error in our SQL query.

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And if you want to pause the video,

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maybe you guys can try to find it first before I go on.

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Okay, let's unpause it.

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So where is the error in my SQL query?

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Basically, what I noticed was that If you look at chats,

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technically you could have more than one chat with the same person, right?

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So if I call this person once,

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twice, they don't pick up.

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Then I call the seller three times, they finally pick up.

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Then technically, I'm actually grouping by call connected,

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which would then mess up my data, right?

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Because I'd have two zeros and then a one.

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So if I group by that,

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then this wouldn't really work out and this data is wrong.

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So what I have to do instead is group by the distinct number of chats and then rejoin it.

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So let's do that again.

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So instead, let me think.

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I still think I can reuse some of my data here.

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So I'd say let's group by the buyer user ID,

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the seller user ID.

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And then let's run actually a function in here where we want to know if there was at least one connection.

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So instead, our actual formula means use audio chat at least once.

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Because here, you know, technically,

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if I'm like talking to this guy and I make two purchases,

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you know, without the audio chat,

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but then I use the audio chat in a separate purchase and I use it at least once,

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but then I chat with him,

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like create like three different chats with that same guy.

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I want to know if at least using it once influenced

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and gives me a higher purchase completion rate than never using it ever.

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This is the bare bones analysis.

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If I use this feature at least once, does it do anything?

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Does it change up the completion rates at all?

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So here we're going to just run a max on call connected.

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So this means that for every buyer-seller combo,

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did they at least connect on a call at least once?

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So I'll label this at least one connection, call connected.

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Then next I'll just do count distinct mp.id same as this one divided by the

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Actually no so instead I'll just use I will also just group by 1 and 2 So as total purchases

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Then I'll wrap this in a subquery with distinct chat as this.

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So we're grabbing the total purchases,

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this is actually completed transaction.

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So we know that we completed this transaction.

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So now I want to group by this value and I can do that with the CTE.

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So I'm grouping by this.

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This is going to be distinct chats.

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And then group by this value, one.

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And then now I can actually just look at the average number of completed transactions.

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And then the sum of completed transactions.

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Okay, cool.

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So why did I make this completed transaction?

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So basically for every combo,

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what this query does is that it basically finds exactly if there is at least one call connected,

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and then if there is a completed transaction.

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So for example, you know,

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one buyer and seller, they didn't connect in a call, no completed transaction.

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Let's say they did complete at least one call and they did complete a transaction.

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So this would be effectively just,

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you know, one because they're only doing one transaction either way so once we take the average of this

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we're taking the average of ones and zeros and

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so that's how we're getting this value of 0.435 or sorry 4.35

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and 3.92 that's this that's the data analytics case question i

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think this is a great kind of solution for now i

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think one last thing i'd like to do is like why don't we try to

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and do an analysis and see if like more call completions lead to more purchase transaction rates.

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So kind of that scenario that I was drawing above,

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except this one is like if we have three audio chats instead of two audio chats instead of one audio chat,

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like does the three audio chats lead to more completed transactions than the one audio chat?

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If it does, then it probably means that audio chats are beneficial for this business.

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So I'll actually leave that for the exercise for you guys.

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If you guys want to see the answer,

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just go to interview query,

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go to the link below,

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and then you'll see the answer in the solution bar right here,

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because I'm going to finish that before this video comes out officially.

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And I hope this was helpful.

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I hope this video isn't all over the place.

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I hope I have a really good video editor that helps me out with this stuff.

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And please remember to like and subscribe on this video

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so I can go through this exercise of doing more videos for you,

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even though, you know, I'm jumping back into it.

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So it's been a painful experience so far,

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but I'm hoping I'll get better and better at it.

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I just need your guys' support.

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Awesome.

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All right?

237

Cool.

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Thanks.

239

Bye.

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