9597

• UCREFRP Catalog Number: 9597
• Author: U.S. Environmental Protection Agency.
• Title: Biological Field and Laboratory Methods for Measuring the Quality of Surface Waters and Effluents.
• USFW Year: 1973.
• USFW - Doc Type: Cincinnati, OH.
• Copyright Material: NO

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BIOMETRICS

1.0 INTRODUCTION

Field and laboratory studies should be well-
planned in advance to assure the collection of
unbiased and precise data which are technically
defensible and amenable to statistical evaluation.
The purpose of this chapter is to present some
of the basic concepts and techniques of sampling
design and data evaluation that can be easily
applied by biologists.
An attempt has been made to present the
material in a format comfortable to the non-
statistician, and examples are used to illustrate
most of the techniques.

1.1 Terminology

To avoid ambiguity in the following discus-
sions, the basic terms must be defined. Most of
the terms are widely used in everyday language,
but in biometry may be used in a very restricted
sense.

1.1.1 Experiment

An experiment is often considered to be a
rigidly controlled laboratory investigation, but
in this chapter the terms experiment, study, and
field study are used interchangeably as the
context seems to require. A general definition
which will usually fit either of these terms is
"any scientific endeavor where observations or
measurements are made in order to draw
inferences about the real world."

1.1.2 Observation

This term is used here in much the same
manner as it is in everyday language. Often the
context will suggest using the term "measure-
ment" in place of "observation." This will imply
a q uan tified 0 bserva tion. For statistical
purposes, an observation is a record representing
some property or characteristic of a real-world
object.
This may be a numeric value representing the
weight of a fish, a check mark indicating the
presence of some species in a bottom quadrat -
in short, any type of observation.

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1.1.3 Characteristics of interest

In any experiment or sampling study, many
types of observations or measurements could be
made. Usually, however, there are few types of
measurements that are related to the purpose of
the study. The measurement of chlorophyll or
A TP in a plankton haul may be of interest,
whereas the cell count or detritus content may
not be of interest. Thus, the characteristic of
interest is the characteristic to be observed or
measured, the measurements recorded, analyzed
and interpreted in order to draw an inference
about the real world.

1.1.4 Universe and experimental unit

The experimental unit is the object upon
which an observation is made. The characteristic
of interest to the study is observed and recorded
for each unit. The experimental unit may be
referred to in some cases as the sampling unit.
For example, a fish, an entire catch, a liter of
pond water, or a square meter of bottom may
each be an experimental unit. The experimental
unit must be clearly defined so as to restrict
measurements to only those units of interest to
the study. The set of all experimental units of
interest to the study is termed the "universe."

1.1.5 Population and sample

In biology, a population is considered to be a
group of individuals of the same species. The
statistical use of the term population, however,
refers to the set of values for the characteristic
of interest for the entire group of experimental
units about which the inferences are to be made
(universe).
When studies are made, observations are not
usually taken for all possible experimental units.
Only a sample is taken. A sample is a set of obser-
vations, usually only a small fractIon of the total
number of observations that conceivably could
be taken, and is a subset of the population. The
term sample is often used in everyday language
to mean a portion of the real world which has
been selected for measurement, such as a water