BOOKS OF RtfiDIfGS - PAHO/WHO

ing of the same patient mix and arrival times. Each day
was repeated 10 times for random service time, with the
same expectations concening random personnel characteristics
(dressing time, transportation time, etc.). Thus,
for cach one of the seven scheduling procedures, there
were:
4 days x 160 dPai'y x 10 repetitions = 6400 patients.
day
Table 5 summarizes the data in relation to this experiment.
It is clear to see that MMWL is superior for all
measures of performance with the exception of two cases.
One case is where the number of patients in the system at
4:30p.m. is 15, while the best (MWL) is 14. The second
case is when the total time for which 95% of patients
complete their service is accomplished in 165 min, while
the best (PS) is 163 min.
Therc is a significant differcncc between CQ, MCQ and
the uther five scheduling methods. In all five procedures,
the examinalion room is assigned to the patient at the time
the person leaves the control desk. The patient moves
physically, and waits at the front of the examination
room. Howcvcr, in rega.rd lo CQ and MCQ, this is not thc
case. The patient has to wait in a common waiting room
until an examination room becomes available. At that
time, the technician returns to the control desk and
determines which patient is next in line and can be
examined in this room. The technician has to identify the
patient and direct the individual to the examination room.
In some instances, the distance may be as great as 50
yards, and the patient may be on a stretcher. It is then safe
to assume that extra activities may take about 5 min which
was incorporated into the model. This fact may explain
the reason that CQ and MCQ did not perform as weil as
theoretical results previously indicated. Once again, this
study demonstrates the possible conflict between queueing
theory and scheduling theory. In scheduling theory,
there is more control on the patients (jobs) in terms of the
arrivais, and service times. In queueing theory, as in the
department described above, there is more randomness.
Waiting time before study
OP
IP
Both
Total time in thce system
OP
IP
Both
No. of patients in system
at 4:30
No. of patients waiting
over 60 min for scrvice
Patient flow analysis and the delivery of radiology service
SPT and TSPT were clearly the most unsuccessful
techniques among the seven procedures. SPT in theory
should produce the best mean waiting time, however, this
result tends to diminish as the flexibility of machine
(rooms) selection increases (see Waysont15]). This
appcars to be the case in the radiology department where
examinations can be performed in several different
examination rooms.
When evaluating the various procedures, attention has
to be given to the feasibility and to the cost of
implementation. The CQ and MCQ procedures can be
implemented manually but would require a considerable
amount of bookkeeping, and a means of scanning the
entire queue to determine which types of examinations
are waiting. In addition, the SPT and TSPT procedures
could also be implemented manually. However, it is
anticipated that certain difficulties would arise in attempting
to implement TSPT manually. Moreover, the MWL
and MMWL procedures will require a computer to
constantly update the expected luad.
SUMMARY AND CONCLUSION
This culmination of observations had desirable results
and a model of the DRD has been developed. The model
has been tested and verified for replication of the
performance of the department at a satisfactory level of
accuracy. In addition, any changes in the department are
tested and verified first on the simulation model.
The model used for the study indicates that increasing
the number of technicians or orderlies will not decrease
patient waiting times, and total time in the department.
Increasing examination rooms, which may be promising,
was considered and rejected because of high costs. It
should be pointed out that decreasing the number of
examination rooms is costly in terms of higher waiting time
and total time. A recommendation was then made that
there is no need for additional technician and orderly staff
to improve service, and that a reduction of the number of
technicians by one will not affect the department's
performance. This is based on the fact that there is no
Table 5. Comparison of 7 scheduling procedures for various measures of performances
Waiting time within which 95% of
palienis reccive scrvice
Total time within which 95% of
patients left the system
'Best value.
'Off by I patient.
'Off by 2 min.
PS MWL MMWL CQ MCO SPT TPST
33
18
23
79
62
68
28
12*
18
75
57
64
26
12'
17*
72*
56'
62'
32
19
23
78
67
71
30
19
23
77
65
69
35
19
24
81
63
70
31
19
29
77
66
70
20 14* 15' 18 18 18 18
16 12 II1' 25 22 20 20
69 64 62* ' 99 93 101 88
163' 172 1652 177 174 188 183
165 -14 -