Introduction to Human Nutrition

Nutrition Research Methodology 317

randomization.” However, when the number of ran-
domized units is scarce, even though each unit may
be large, there would be no guarantee that the groups
to be compared would be identical. Conversely, if the
randomization has been done on an individual basis
and the whole sample is large enough, a random
scheme will usually accomplish its objective of dis-
tributing the participants in groups that are essen-
tially homogeneous in all measured and unmeasured
factors. This balance makes groups directly compa-
rable and ensures the validity of causal inferences
extracted from a randomized design (individual
randomization).
In general, experimental studies with individual
randomization provide the strongest evidence for the
effect of an exposure on an outcome. Experimental
studies are the inferentially strongest designs to
demonstrate causality, but they may raise substantial
ethical problems because the scheme of random
assignment is used to help not the subject, but the
experiment. Subjects are exposed only to meet the

Box 13.3 Sample ethics form for completion prior to research

The proposal respects the fundamental ethical principles including

human rights and will deal only with individuals adequately

informed and willing to participate. Also, all research data partners

will obtain national authorization from an ethical committee or

equivalent body before any intervention with subjects. The study

does not involve any genetic manipulation.

● Requested specifi cations:

● Human embryos or fetus No Yes

● Use of human embryonic or fetal tissue No Yes

● Use of other human tissue No Yes

● Research on persons No Yes

● If yes, further specify if it involves:

● children No Yes

● persons unable to consent No Yes

● pregnant women No Yes

● healthy volunteers No Yes

● Use of nonhuman primates No Yes

● Use of transgenic animals No Yes

● Use of other animals No Yes

● Genetic modifi cation of animals No Yes

● Genetic modifi cation of plants No Yes

● Other specifi cations:

● The regulations, concerning human and medical research,

will be respected with precise reference to the recommenda-

tions of the Helsinki (1964), Tokyo (1975), Venice (1983) and

Hong Kong (1989) committees, as well as other EU regula-

tions RD 561/1993, 65/65 CEE, 75/318 CEE, Directive 91/507

and 89/843 EN-C (ISBN 92-825-9612-2).

needs of the protocol of the study and not the indi-

vidual needs of the participant. Therefore, random-

ized experiments with humans can only be conducted

under strict ethical conditions (see Boxes 13.3 and

13.4). It is not permissible to carry out experimental

studies where the exposure is potentially harmful.

Therefore, under these conditions, nonexperimental

(observational) study designs must be applied. The

design options in nutritional epidemiology must take

into account the setting, uses, advantages, and limita-

tions (Table 13.7).

Experimental designs in epidemiology

Experimental epidemiologists try to conduct con-

trolled studies, and in these studies it is the investiga-

tor who assigns the exposure. Human studies, however,

unlike animal studies, involve aspects that the inves-

tigator cannot control. This is particularly so when

they are carried out on a free-living population. Two

study designs dominate this area of epidemiology:

randomized controlled trials and crossover studies.

In these studies, subjects are randomly assigned to

Box 13.4 Sample of an informed consent form

This form will cover the following aspects:

I ................... (name)

I have read the volunteer’s information

I have felt free to make questions concerning the study

I have received enough information

I have talked to the following personnel responsible (names... )

I understand that my participation is on a voluntary basis

I understand that I can withdraw from the study:

1. If I wish


2. Without further explanations
   Therefore, I freely confi rm my availability to be involved in the
   trial
   Date
   Signature
   In addition, all the partners agree with the following statement
   In implementing the proposed research I shall adhere most
   strictly to all national and international ethical and safety
   provisions applicable in the countries where the research is
   carried out.
   I shall conform in particular to the relevant safety regulations
   concerning the deliberate release into the environment of
   genetically modifi ed organisms.