How to interpret charts and data in case interviews

case interview charts and exhibits

90% of consulting case interviews will have you interpret charts and data or 100% of top-tier firm interviews such as McKinsey, BCG, and Bain.

This article is part of our consulting case interview series. For the other articles, please click below:

Charts and exhibits in consulting case interviews

Charts visually represent data in the form of points, bubbles, lines, bars, and pies amongst others. Tables contain data in an organized manner. Using both tables and charts can display values measured in a company (e.g., sales data), in a market (e.g., market growth), etc. Specific types of charts are better suited than others for different uses.  However, during the case interview, you are often not presented with the best available or most suitable chart format. 

Many candidates struggle with this part of the case interview, similar to the case interview math questions. In fact, being able to quickly skim through a wide range of data, elicit the key information, and derive top-down what it means for the question at hand is a key skill that all major consulting firms are looking for in candidates.

You can train this skill and improve your analytical approach to data tables and graphs and along the way improve your overall performance in the case.

Types of charts in case interviews

The good news for you: Firms such as McKinsey, BCG, and Bain always use the same types of charts in their case interviews as well as on the job.

Below is an almost exhaustive library of all charts and common variations you should expect during the case interview, covering 99% of what we have seen in interviews, on the job, and from colleagues.

More often than not, you will be presented with more than one chart and have to interpret and find the key insights by combining the two. Also, sometimes charts can be combined and a bar chart could also contain a line or two from a typical line chart.

As a side note: We have populated the charts with random numbers and random legends to make them appear more realistic as they would look like in a case interview. In practice, each chart can display many things.

Bar charts

Bar charts are most commonly used when comparing values of several items at a specific point in time, or 1-2 items at several time intervals. Too many items or time intervals have a negative impact on the readability.

One variation you might come across in case interviews is the stacked bar chart. It extends the standard bar chart by one or more categorical variables. Each bar is divided into two or more sub-bars, each one corresponding to a different categorical variable.

the image displays a bar chart from a case interview as it is typical for mckinsey, bcg and bain
A typical bar chart in a case interview

Another variation of the bar chart is the 100% bar chart. It’s a stacked bar chart that shows the relative percentage of multiple data series in stacked bars, with the total of each full bar always equalling 100%. Be aware that, while all bars have the same height visually, they do not necessarily have the same total.

the image displays a 100% bar chart from a case interview as it is typical for mckinsey, bcg and bain
A typical 100% bar chart in a case interview

The clustered bar chart visualizes multiple sets of data over the same categories (like revenue of two products over three years).

the image displays a clustered bar chart from a case interview as it is typical for mckinsey, bcg and bain
A typical clustered bar chart in a case interview

Bar charts are less suitable to illustrate parts to visualize parts of a whole unless they come in a waterfall chart form. A waterfall chart can be either build up to a total or build down from a starting point to a new ending point.

the image displays two waterfall charts from a case interview as it is typical for mckinsey, bcg and bain
Typical waterfall charts in a case interview

A specific form of a bar chart would be a histogram, which displays an approximate representation of the distribution of numerical data. Histograms can be used to provide insights into mean and standard deviation.  

Line charts

Line charts illustrate time-series data, i.e development, and trends in data over a specific time period. Contrary to bar charts, they consume almost no space since the points in time are connected by lines, which allows visualizing a large number of time intervals.

the image displays a line chart from a case interview as it is typical for mckinsey, bcg and bain
A typical line chart in a case interview

They are not used to show data break downs and tend to become confusing with more than 5 simultaneous variables (lines).

Pie charts

The pie chart’s core strength is to visualize proportions. They include all parts of a whole, without any overlap in their segmentation. Pie charts can also be displayed as donut chars (same, just with a hole in the middle).

the image displays a pie chart from a case interview as it is typical for mckinsey, bcg and bain
A typical pie chart in a case interview

Time series cannot be displayed with pie charts.

Scatter plots

Scatter plots visualize how two variables relate to each other by plotting data points on a matrix. They are an extremely powerful tool to look at the correlation of variables by being able to display an infinite amount of data points, while still keeping readability.

the image displays a scatter plot and a bubble chart from a case interview as it is typical for mckinsey, bcg and bain
A typical scatter plot (top) and bubble chart (bottom) in a case interview

Scatter plots are limited by the number of axes (e.g., two axes can display two variables).

The bubble chart is a variation of the scatter plot that allows displaying the size of a certain data point, thereby introducing a third variable into the picture. The size of the bubble can visualize many things. It usually shows much fewer data points than a scatter plot.

Flow charts

Flow charts or process charts visualize a process or a system and its individual parts. They can be used to describe, improve, and communicate simple or complex processes in clear and easy-to-understand diagrams.

How to interpret charts and data in case interviews

In order to interpret charts most effectively and find their ‘so-what’ to impress the interviewer, here are a few habits you should internalize and apply whenever you are asked to interpret some data in the form of tables, graphs, etc.

Zero in on the key bits of information

To interpret a table or chart, read the title, look at the units and labels, then derive the key insight. Study the graph to understand what it shows within 15-30 seconds. Not all information on the papers you get is insightful or important and some might even be misleading. Parts of the information hidden in the charts is crucial, others just create noise to distract you. Often they contain decoys that trick you into faulty conclusions or logic.

The key is to filter out the one or four key messages or outliers, most striking when looking at it first. There will always be other things you could infer but in the interest of time, that would likely not be relevant for the case recommendation (think 80/20).

The key messages hidden in the data and charts is usually one of the following:

  • Some number or group of numbers is very small or very large compared to the others (internal vs. market, internal vs. specific competitor, internal vs. other internal,…) – basically a comparison of patterns and correlation (often a bar or a line chart)
  • Some number or group of numbers show high growth or low growth compared to the others
  • There is a specific trend or trend reversal (usually a line charts)
  • There is a specific relationship or (negative) correlation between two or more numbers
  • There are absolute or relative changes in one value vis-a-vis some comparable values
  • On average, the numbers look good, however, when digging deeper into specific segments we see certain issues or deviations

Make sure to spot those kinds of patterns quickly. When you are given two or more charts/ tables the key insight usually comes from combining both.

Communicate top-down

Whenever you present an insight during a case interview you should communicate your findings top-down. The same is true when presenting your interpretation of a chart, table, graph, etc. Start with the single most important fact you can extract from the chart.

  1. Give the answer or the key insight the interviewer is looking for
  2. Then, provide supporting evidence in a logical sequence. Substantiate your findings with strong arguments from the data. You want to build one or more pyramids with the findings on top and the facts that substantiate it as the base.
  3. Discuss the ‘so-what’ for the client problem you are trying to figure out and find a recommendation for. Tie those findings to the case and your analysis and interpret their implications.

Don’t start going in circles; don’t go astray. Stay structured and hit the interviewer with the key points. The interviewer mimics the client and senior clients usually don’t have much time to spare. Every sentence in the chart interpretation part should add value to your analysis. Stay away from empty words and phrases or worse aimless rambling.

By setting your communication up that way, you demonstrate that you are able to

  1. Are able to retrieve key insights in a data set quickly
  2. Communicate top-down with senior executives
  3. Consider the impact of the data on the current issue

Also, you give the interviewer a chance to dig deeper to understand your reasoning. In that case, you could present more details fitting your train of thought.

Avoid common pitfalls

Stay away from the following common pitfalls and you will already fare better than 80% of case interview candidates we have interviewed.

  1. Starting to talk about the data without prior thinking, basically figuring out insights along the way without proper structure
  2. Quickly finding the insights, but then keep rambling on until the interviewer has to step in and ask the candidate how to proceed
  3. Failing to recognize or mixing up units and magnitudes, especially across charts and tables
  4. Failing to properly identify the units, labels, and different axes
  5. Failing to interpret the key insights in the context of the case at hand
  6. Lacking a proper so-what of the key insights and not explaining the implications of the data
  7. Messing up computations along the way (see here for our guide on case interview math)

Train chart interpretation

You can quickly improve your chart interpretation skills by applying the case interview tips above. Prepare for McKinsey, BCG, and, Bain case interviews by analyzing charts in magazines such as The Economist or the Wall Street Journal. To check your insights, compare them with the text short articles accompanying the charts.

Click here to get to the ever-expanding collection of the Economist Daily Charts.

In addition, establish a case interview math practice routine, since case math is often based on the exhibits you will receive during the case study interview. Learning about chart interpretation and consulting math should be key priorities in your case interview prep.

How to improve your case interview skills

If you want to improve your case interview and problem-solving skills and learn the key habits and tricks that make you succeed in any McKinsey, BCG, and Bain interview, try our case practice, the prime resource for top-tier consulting interviews.

Together, we spent 9 years with McKinsey and coached 100s of candidates to receive their desired offers. Our mock interviews have a 100% satisfaction rate and 9 out of 10 candidates that go through our Ready-for-McKinsey coaching program receive the offer. If you want to get the same knowledge in an extensive 40-part video series, check out our Ready-for-McKinsey video academy.

If you want to go deeper to brush up on your math and chart interpretation skills, we have created a program with detailed insider learning materials, 25 videos, and a guidebook as well as 2,000 practice drills (including common case interview question and answers) that mimick the McKinsey, BCG, and Bain case interview math as well as the aptitude and analytics test math for you here: the Case Interview Math Mastery.

We are consistently ranked as the best McKinsey and MBB coaches on PrepLounge.

 

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