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TABLE 1. SELECTED SOURCES OF INFORMATION PERTAINING TO VARIOUS CONSUMER PRODUCT CATEGORIES

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The analysis of the data obtained and the development of relationships between product durability and those factors which impact upon it were found to be within the scope of traditionally employed statistical methodologies. However, the use of these methodologies is expected to be restricted over the short-run because of various problems associated with the available data base. These problems are of the following form:

a. Most of the available data are qualitative rather

than quantitative.

b. The available quantitative data cover only a limited

C.

time span.

The conditions under which a specific product was
operated are not always known and are not uniform.

for comparison purposes across the product category.
d. The stated in-service period for a particular pro-

duct does not necessarily reflect its true useful
life; (e.g., some heavy construction equipment is
depreciated over a short time span for a specific
project.)

e. Maintenance records, repair records and associated

costs are not usually available for most products.

The form and nature of currently available data are discussed

next. An analytical treatment, illustrating the use of various statistical techniques, is also presented.

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2.1 Data Acquisition

As stated above, data were not available for all of the study product categories and, of those which were available, not all were quantitative in nature. The form also varied, ranging from information which clearly qualified the existing data (e.g., for construction equipment) to that which is collected on an intermittent basis as part of consumer surveys, and is therefore of inferential value. These data characteristics (nature and form) are described for the following product categories

2.1.1 Heavy Construction Equipment

Of all the product categories studied, we found that
the best information and data existed for heavy con-
struction equipment. This information is well docu-
mented by various manufacturers and is intended pri-
marily for use by contractors in their development
of operating costs and depreciation rates for equip-
ment for specific projects. For example, Table 2
presents the estimated depreciation period* for vari-
ous types of construction equipment according to appli-
cation and operating conditions. A similar analysis
for tire life, for a particular type of equipment,

* This period is not necessarily equivalent to physical life.

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Track-Type
Tractors

Pipelayers

Wheel Tractor
Scrapers

Off Highway Trucks

What! Type
Tracters,
Compactors

Wheel Loaders

Track Type
Loaders

Motor Graders

TABLE 2.

GUIDE FOR SELECTING DEPRECIATION PERIOD BASED ON
APPLICATION AND OPERATING CONDITIONS

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Source: Caterpillar Tractor Co.

23-615 073 11

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i.e., motor graders, is shown in Figure 1. The com-
bination of these data elements with information per-
taining to repair factors based on specific operating
conditions (Table 3) permits the development of esti-
mated owning and operating costs. Table 4 is an ex-
ample of the way in which these data are used in esti-
mating such costs for a track-type tractor.

A summary of average physical life, for various major
types of construction equipment, as estimated by con-
tractors and equipment distributors is presented in
Table 5. Although these estimates are based on a
1963 survey, it is believed that they are still repre-

sentative.

2.1.2 Tires

There are several variables which have a marked effect
on the performance and durability of tires. These
variables include both the type of construction and
kind of materials used. For example, the ply, tread
width, rubber composition, and nature of accessory
material (nylon, polyester, steel) are all important
influencing factors. Also, there is a demonstratable
trade-off between performance and durability whereby
materials that display better gripping characteristics
result in concessions in terms of tread life. Currently

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