There are typically two primary ways to approach problem-solving - "
top-down" and "
bottom-up". In this post I'll explain the differences as well as why the
top-down approach is preferred by McKinsey bosses and interviewers...
McKinsey takes a
structured approach to
solving problems that includes
breaking down larger issues into smaller pieces. Those components of the problem are arranged into an "
issue tree" with the biggest, overarching issues at the top. Those are then supported by additional, increasingly specific, tactical, broader levels of
supporting details. I will devote a future post to these issue trees.
Top-Down Approach
This means the problem solving begins at the "top" or with the
highest-level, overarching question or theme, also known as the
governing thought. From there, the problem is broken down, identifying and developing the elements the next level down, with special focus on the
critical or vital few drivers of impact. Only after those key elements have been determined does the focus shift to
tactical details. The process is repeated, adding additional levels down the tree the tree is
exhaustive.
Bottom-Up Approach
This is the opposite of the top-down approach and, as the name implies, begins with the
tactical, granular, specific details. In this case, the work focuses on starting with a
laundry list of issues, then organizing them into like groups, or "
buckets". Those buckets can often be grouped further,
building levels up the tree, until, finally, the key drivers and governing thought are reached.
Top-Down vs. Bottom-Up Thinking
The simplest way to summarize the difference is this: working at the top is considered
strategic, while working at the bottom is
tactical. McKinsey consultants are encouraged to think strategically vs. tactically. Here are some reasons why...
Why the Top-Down Approach is Preferred
There is a strong bias toward top-down thinking at McKinsey because it a) is
logical,
with a
structured approach and b) starts by defining the
most important questions and issues
first. The assumption is that if enough smart, experienced, hard-working consultants and clients
align on the governing thought, the rest of the work that follows will be
directionally correct.
Working top-down helps ensure that the questions asked and issues raised are
completely exhaustive. Less relevant ones might eventually get
trimmed, but they will at least have been considered. Top-down thinking also
limits wasted work because only those topics deemed relevant and important to the governing thought need to be developed in detail.
Why the Bottom-Up Approach is Not Preferred
Starting at the bottom introduces several challenges. First, it's not immediately clear - and might never be - if important details or areas have been
missed or
under-represented. Second, items can be bucketed in a variety of ways that might all seem correct, but could be
sub-optimal and/or lead to very different governing thoughts. Finally, there's just a lot
more work to be done at the bottom of the tree where there are countless details that can be considered and developed.
A Common Exception - Excel Modeling
One noteworthy exception when the bottom-up approach is often seen as
superior to the top-down approach is in
Excel modeling. While a top-down approach to quantitative questions is helpful at the beginning of an engagement or workstream to get a
directional sense of what the final answer will be, using that approach with clients and/or a final answer runs the risk of coming across as
naive or just plain
wrong. Instead, a bottom-up model is required to
confirm and
support the final answer.
