How to interpret charts and data in case interviews

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:

• Overview of case interviews: what is a consulting case interview?
• How to create a case interview framework
• How to ace case interview exhibit and chart interpretation (this article)
• How to ace case interview math questions

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.

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

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.

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.

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).

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.

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 we can help you ace the MBB interviews

We have specialized in placing people from all walks of life with different backgrounds into top consulting firms both as generalist hires as well as specialized hires and experts. As former McKinsey consultants and interview experts, we help you by

• tailoring your resume and cover letter to meet consulting firms’ highest standards
• showing you how to pass the different online assessments and tests for McKinsey, BCG, and Bain
• showing you how to ace McKinsey interviews and the PEI with our video academy
• coaching you in our 1-on-1 sessions to become an excellent case solver and impress with your fit answers (90% success rate after 5 sessions)
• preparing your math to be bulletproof for every case interview
• helping you structure creative and complex case interviews
• teaching you how to interpret charts and exhibits like a consultant
• providing you with cheat sheets and overviews for 27 industries.

Reach out to us if you have any questions! We are happy to help and offer a tailored program to help you break into consulting.