Reducing the Phone Bill
with Minitab
Or How I Learned to Love Garage Sales
Steven Maley
Continuous Improvement Training Program Manager
Textron Aviation
1
Please silence your cell phone.
Background
► Year: 2003
► Husband & father of
young family
► Location: Wichita, KS
► Completed 6 month
Textron Six Sigma
Black Belt program
► Recently obtain cell
phone
► Selected ‘Family Plan’
option
► Initial bills were as
expected
3
Problem
► April phone bill more
than expected
► May phone bill more
than expected
► June phone bill more
than expected
► Wife’s view of
problem:
There is a problem with
our cell phone plan, and
this is known because
current minutes are not
enough for the family
over the past 3 months.
► Per training, problem
statement = solution in
disguise
A conflict opportunity arises…
4
Goal
► Found common ground
► Agree last 3 months bills
too much
► Focus on alternatives
► Agreement on unknown
reason going over plan
minutes
► Revised problem:
There is a problem with our
cell phone usage, and this is
known because the minutes
are over the plan for the
past 3 months, leading to a
strain on the family budget.
► Agreed goal:
Identify root cause of
overage minutes.
5
Investigation with Minitab
► Began analysis late
Friday evening
► Downloaded log
from provider’s site
► Step 1: Usage by
user
► Findings:
Wife uses 4 minutes to
every 1 of mine
► Not surprised, I have
work phone
Next: Wife’s usage over time…
6
Individual Call Duration
Daily Call Duration
Stability Investigation
Stability Investigation
Daily Call Duration
Wife’s Usage Over Time
► Findings
Individual call duration
doesn’t fit a common
distribution
Fail to reject √(Daily
minutes) come from
normal distribution
√(Daily minutes) contains
‘special cause’
Daily minutes sub-grouped
by week have no ‘special
cause’
Compared to other days of
the week, Thursday has
greater average daily
minutes and variance
Next: Wife’s callers over time…
Further Minitab Investigation
► Pareto of wife’s callers
GREAT CAUTION SHOULD BE USED HERE
13
Analysis Review Meeting
► Took results to bedroom
► Wife’s habit: reading in bed
► Asked who was most common number
► Answer: wife’s girlfriend, explaining Thurs calls
► Girlfriend’s provider was different than ours
► Each took turns shopping garage sales on opposite
sides of town for children’s clothes
► Realization: A few calls costing $ saved $$$ in
children’s clothing
► Decision: Move to next number
► We didn’t want to change providers, so why would
they
► The friendship was paying off for itself
14
Next Number Discussion
► 2nd Most frequent: my mother’s ‘land line’
► Instant concern about discussion
► Talks arranged childcare
► Mother’s cell phone with same provider
► Wife stated mother never answered cell phone
► Visited mother next morning
► Loved cell phone on weekends
► Call old friends during breakfast
► Minutes were free
► Hated phone during week
► Phone would ring
► No one on the line when answered
Next: Mother’s movements
15
Spaghetti Diagram
Spaghetti Diagram
► Findings
Mother loves television
Travel duration > 3 rings
Cell phone sent call to
voice mail after third
ring
Mother only made
outgoing calls or
received incoming calls
‘Voice mail, what’s
that?’
‘Son, there is no
answering machine
connected to this
phone.’
17
Job Instructions
► When receiving call
on weekday:
1. Go to cell phone
2. Pick up phone
3. Press green button
twice
4. Wait for person who
called to answer
phone
July Phone Bill
Results
► To this day, calling my mother:
1. Call her cell phone
2. Let it ring 3 times
3. Hang up
4. Wait for her return call
► Defining the problem, Minitab analysis, a
spaghetti chart, and simple job instructions:
► Mother happier with her phone
► Wife able to arrange child care with one dialing
► 2nd largest bar in Pareto chart went to near 0
► Monthly minutes for next month and for quite
some time was below planned minutes
Then daughter got a cell phone and a texting issues began…
20