Page 41 - Six Sigma Demystified

22 Six SigMa DemystifieD

In practice, it is useful to think of metrics as big Y’s and little y’s. The little
y’s are the drivers of the big Y’s. Mathematically,

Y = function of {y , y , . . . , y }
1
2
n
1
Y = function of {y , y , . . . , y }
1
2
n
2
. . .
Y = function of {y , y , . . . , y } for m big Y’s
n
m
1
2
Big Y’s and their corresponding little y’s are defined at each level of the
organization— the business level, the operations level, and the process level.
The transfer functions (or flow- down functions) provide a means of understand-
ing the relationships between the process- level metrics and the bigger- picture
organizational metrics that guide the business operations and the Six Sigma
program.
Starting at the business level, then down to the operations level, and finally
the process level, the little y’s at each stage become the big Y’s at the next stage
down. While the big Y’s are useful for tracking, the little y’s provide the detail
necessary for controlling processes and improving the organization.
This flow-down of the metrics from one level to the next provides direct
linkage of the operational and process metrics to the key stakeholder big Y
metrics used in the dashboards at the business level.
For example, the big Y’s related to the customer stakeholders’ group may be
as follows:
Y = satisfaction score
1

Y = retention rate
2

Y = order turnaround time
3

Y = sales revenue
4
The metrics at this level provide a good high- level stakeholder view but do not
yet provide the details necessary to optimize operations. It would be helpful to
drill down on each of these big Y’s to understand their little y drivers. Con-