Proceedings of the EuSpRIG 2019 Conference “Spreadsheet Risk Management” ISBN : 978-1-905404-56-8
Copyright © 2019, EuSpRIG European Spreadsheet Risks Interest Group (www.eusprig.org) & the Author(s)
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2 Recruiting the participants
An invitation to participate in the challenge was sent to the EuSpRIG mailing list(EuSpRIG, 2019)
and on the LinkedIn Excel Developers group(LinkedIn, 2019), with encouragements to redistribute
the invitation in other circles. The challenge lasted one month from November 1 to November 31,
2018. The participants had to request the kit by email, which allowed us to measure the interest level.
There were 109 kit requests and 17 of them submitted a spreadsheet. We did not investigate why
potential participants did not complete the challenge, but some did communicate that they were too
busy or that they found the problem too complicated and did not know how to implement it.
The participants were given a problem along with its solution: all the variables and the formulas were
presented in the Formula List. Their task was not to solve the problem, but to implement its given
solution. The participants were free to use any feature that did not require non-standard features: it
had to work in a simple Excel installation.
The Formula List contains 5 variables with more than two dimensions.
MSP Unit Sales
and
MSP
Sales Amount
are in the (Month, Sector, Product) dimension set,
MSPR Unit Sales
and
MSPR
Variable Cost
are in the (Month, Sector, Product, Region) dimension set, and
MPR Unit Sales
is in
the (Month, Product, Region) dimension set. Those are the variables that interested us in this analysis.
3 Initial analysis
Given the voluntary lack of directives, some participants did not implement all the variables of the
Formula List. They avoided implementing some multidimensional variables by building more
complex formulas. For example, the two four-dimensional variables,
MSPR Unit Sales
and
MSPR
Variable Cost
can be avoided by changing the given formulas for the variables that depend on them:
MPR Unit Sales
,
Monthly Unit Sales
and
Monthly Variable Cost
. So, the formulas
MPR Unit Sales = SUM( MSPR Unit Sales )
and
MSPR Unit Sales = MSP Unit Sales * Region Sales Distribution per Sector
were combined by some participants to calculate
MPR Unit Sales = SUM( MSP Unit Sales * Region Sales Distribution per Sector ).
This was unfortunate for this study, as we were interested in seeing how the variable
MSPR Unit
Sales
was implemented in their worksheet. But since the four-dimensional variables were not
presented as output variables in the Interface sheet their implementation was mathematically correct.
4 Implementation strategies
The implementation strategies used by the participants can be assigned to two broad categories that
we'll call the Database approach (DB) and the Variables and Formulas approach (VF). The VF
approach is well used in one or two-dimensional spreadsheets in business and finance applications.
In a one-dimensional spreadsheet, the variables, like Unit Sales, Cost and Revenues, are usually
represented in rows, with columns on the left-side documenting them with their name and, sometimes,
their units. One dimension, like Month or Region, is presented in a row at the top and columns
represent the instances of the dimension, such as Jan, Feb, Mar or South, North. The formulas appear
in a rectangular shaped area below the dimension row and to the right of the variables. Normally, the
formulas linking the variables are written for one instance of the dimension and then copied under the
other instances to the right.
Implementing two dimensions starts to be a bit more involved. One method consists of presenting the
second dimension along with the first one. All the instances of the first dimension are then repeated
for each instance of the second dimension. Thus, if we have twelve months and three regions, the set
of twelve months (Jan, Feb… Dec) will be repeated for each of the three regions, giving 36 columns.