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© 2014 Pacific Crest
409
Step
Explanation
Watch it Work!
1. What is your
purpose?
Identify what you want to learn from
the use of the model as well as what
the problem is that you want to solve
How do you calculate a tip, especially
within a group, and quickly determine
what the appropriate tip is in any
situation?
2. What is the
designer's
purpose?
Determine the motivation of the
designer and why they built the
model
iTipping.com serves as an independent
researcher in tipping etiquette. Google
provides a calculator model as a benefit
to users of their site.
3.
Are the
purposes
aligned?
Determine if the chosen model is
appropriate to meet your purpose
and not biased
The calculations and suggested tip rates
agree with current social norms.
4. What are the
inputs?
Inventory all the input variables
associated with the model
Both models use the cost of the meal,
with taxes included, and a tip rate. The
calculator model also uses the number of
people splitting the bill.
5. What are the
outputs?
What are the different
representations of the results and
which variables do these results
describe
Provides the option of a single
recommended tip amount or possible
ranges for tips (if you want to qualify the
tip based upon service quality)
6. What are the
relationships?
Describe the mathematical
relationships used to justify the set
of outputs produced, given a set of
input values
The tip is the total bill multiplied by the tip
rate divided by the number of people.
7.
Does the
model make
sense?
Explore enough situations (what ifs)
and compare the variation in the
outputs as you change the inputs
and determine if the model makes
sense based upon expected results,
empirical evidence, and experience
Increasing the total bill or tip rate causes
a proportional increase in the tip amount.
Increasing the number of people causes
a proportional decrease in the tip amount
per person.
8. What are the
limitations of
the model?
In which situations (range of inputs)
will the model not give reliable
results or fail to address a critical
input variable?
The table allows two tip rates and a
limited number of specific bill amounts.
The calculator accepts any bill amount,
rate, and party size. The models do
not handle the situations where the
party is 6 or greater and a tip is already
included, the service is either superb or
substandard, or the locale’s standard
for tips (NYC or outside the U.S.) are
inherently different.
9.
Can you
validate the
results so you
can trust the
conclusions?
Did you meet your learning
outcomes and did the model reliably
solve your defined problem? What
is your confidence level?
I am now an excellent tipper, not in
amount but in skill, and I know how
and when to use either model with
confidence.
9.1 Analyzing and Using Mathematical Models