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FIELD TRIALSELISHA JR

UNIVERSITY OF DODOMATANZANIA

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FIELD TRIAL• Field trial is the one of types of interventional study designed to evaluate

prevention strategies. They are carried out to people who do not necessarily have a particular disease but are considered at risk.• These studies are also referred to as preventive studies and may take the

form of a trial to test health education methods , training procedures or other public health programs.• A field trial involves evaluation of whether an agent or procedure reduces

the risk of developing disease among those free from that condition at enrolment.• Because these trials involve healthy rather than diseased people, they tend

to be logistically more difficult to carry out than clinical trials.

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• Field trials are generally have to be conducted in the ‘field’ rather

than in hospitals or clinics.• Field trials can be carried out among individuals or groups of people • The group may be a household, a block of houses, a school or a whole

community.• Field trials in which whole communities are the unit of allocation are

called community trials .

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Example of individual intervention field trialA randomized trial was carried out among Whitehall (English) civil servants to measure in middle-aged men the health effects of stopping smoking. A total of 1445 male cigarette smokers aged 40–59 years who were at a high risk of developing cardiorespiratory diseases were randomly allocated to intervention (714 men) or normal care (731 men). Those in the intervention group received individual advice on the relation of smoking to health. Most then expressed their wish to stop smoking and received further support over the next 12 months. The two groups were then followed up for twenty years (Rose & Colwell, 1992)

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Example of group interventional field trial• The Community Intervention Trial for Smoking Cessation (COMMIT)

was a multicentre project designed to evaluate a communitywide smoking cessation programme in the USA. This trial began in 1989 in 11 matched pairs of communities. One community of each pair was randomly assigned to receive the smoking cessation programme with the other acting as a control. The intervention was designed to promote smoking cessation by using a wide range of community resources to affect attitudes and policies towards smoking (COMMIT Research Group, 1991).

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• There are various reasons for selecting groups rather than individuals

as the study unit. • Many interventions are impossible to assign at an individual level. • Environmental interventions such as water fluoridation or

improvement of air quality can be conducted only at a group level.• Most health education interventions also fall into this category

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Community trials• Field trial in whole populations (communities) are usually referred to

as community trials or community intervention studies.• Community trials focuses on mass education campaigns aimed at

changing people’s knowledge and attitudes.• Community intervention studies, the exposure is usually given to

subjects (for example, by vector control to reduce malaria, pit latrines for clean water), or to reduce work load and/or to increase disposable income.

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These community intervention studies can be characterized as:(1) explicitly nutritional (a) nutrition oriented food programs (b) feeding programs (c) weaning foods (d)fortification (e) nutrition education;(2) non- or implicitly nutritional (a) health related, e.g. immunization, sanitation; (b)economic, e.g. income generation or substitution; (c) labor-saving.(3) integrated

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STUDY DESIGN• Intervention studies are generally time consuming and costly. They cost more than

observation studies as they normally require dedicated staff to coordinate them (personnel to evaluate and recruit patients, carry out follow up, etc.)

• It is even more important to clearly define the research question to be answered and estimate how great an effect must be observed for the intervention to be deemed successful.

• It is not always possible, desirable or ethical to carry out an intervention study and not all health care intervention can be assessed in this way. There must be sufficient doubt about the benefits and risks of a new intervention compared with the usual or no treatment for it to be considered ethical to allocate participants to one or other group.

• Another major consideration for an intervention study is the sample size required.

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Selection of study population• Those who are eventually found to be both eligible and willing to enroll in

the trial compose the actual study population and are often a relatively small and selected subgroup of the experimental population.• Participants in an intervention study are very likely to differ from non-

participants in many ways that may affect the risk of development of the outcomes under investigation. • Whether or not the subgroup of participants is representative of the

entire experimental population will not affect the validity of the results of a trial conducted among that group. It may, however, affect the ability to generalize those results to either the experimental or the target population.

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Allocation of treatment regimensIn any intervention study, the investigator will allocate the participants either to the intervention group, which will receive the therapy or preventive action under study, or to the control group, which will receive the usual or no treatment. The two groups are then compared on outcome of interest. To avoid any underlying differences between the two groups affecting the outcome, it is important that the groups are similar in all other respects.

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Random allocation• Random allocation is the best method of allocating the study subjects

to the different study groups. This method allows chance, and only chance, to determine the assignment of subjects to the various groups• It is, therefore, the only way of ensuring that any differences in the

outcome measures of the trial are due to the effects of the intervention rather than to underlying differences between the groups.

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• Randomization eliminates selection bias on the part of the participants and investigators• Randomization tends to create groups that are comparable in terms

of the distribution of known and, more importantly, unknown factors that may influence the outcome.

Randomization has two major advantages in relation to other methods of allocation.

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1. Simple randomization• Simple randomization is the most elementary method of

randomization.• It is the equivalent of tossing a coin. However, randomization by

tossing a coin should not be used because it cannot be checked or reproduced.• One of the disadvantages of simple randomization is that it may result

in markedly unequal number of subjects being allocated to each group just by chance

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2. blocked randomization• This method guarantees that the numbers of participants allocated to

each study group are equal after every block of so many patients has entered the trial. Suppose that patients are going to be allocated to treatments A and B in such a way that after every fourth subject there are an equal number of participants on each treatment.• The combination for a particular block of four patients is chosen at

random from the six possible it would mean that patients would receive treatments ABAB, ABBA, BAAB and BABA, respectively.• This procedure thus allocates eight patients to group A and eight to

group B

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3. Stratified randomization• When the results of the trial are likely to vary between, say, the sexes or

different age-groups, stratified randomization should be used. In this situation, strata or groups are formed and randomization occurs separately for the subjects in each stratum.• As subjects become eligible for inclusion in the trial, their appropriate

stratum is determined and they receive the next random-number assignment within that stratum.• Stratified randomization has the advantage of assuring balance between the

groups, at least on the characteristics that determine the strata. • The disadvantage with stratified randomization is that it is administratively

difficult and cumbersome to execute

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Efficacy and Effectiveness• All trials test the efficacy of an intervention and assess the

effectiveness.• The Field Trial it evaluate efficacy of intervention designed to prevent

disease, e.g., vaccine, vitamin supplement, patient education

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Measuring the outcomes• Measurement (or reporting bias) can be minimized by blinding trial

investigators and participants to the allocated treatment. If both the investigator and participant are blinded, the study referred to as double-blind. If it is either the participant or investigator that is blinded, the study is single-blind.• Sometimes it is not possible to keep the allocation of the intervention

hidden from the participant or the investigator. For example, if the study is to compere the effect of mosquito nets versus antimalarial tablets, then the participant will know which intervention they are receiving, although it might still be possible to keep allocation of groups from microscopists who analyse the blood samples.

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Analysis• The main method of analysis of an intervention study should be by intention to treat.

This means that the analysis should include results from all study participants by the groups to which they were allocated at the start of the study, even if they swapped groups or subsequently dropped out of the study.

• This method avoids potential biases that can arise from different levels of participation, and also because non-participants are usually different from those who complete a study in terms of their risk of side effects.

• It also ensures that the study is relevant to the real world since if only individuals who complete their treatment are included in the analysis, the study will not necessarily be an accurate representation of what will happen when the intervention is used in general population, in whom compliance is rarely, if ever, 100%. It is of course possible to analyze a study for only those who receive and complete their treatment regimen, but this should always be clearly stated when the results of the study are reported.

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Interpretations• Once the results have been analysed, the investigator need to decide

whether the results are wholly due to the intervention or whether they could be explained by other factors. • If the trial has been carried out correctly, and the randomization and

blinding procedures are effective, then there should be few problems with bias and confounding. • It is important to distinguish between results that are statistically significant

and those that are clinically significant. It may be that a result has reached statistical significance but because of other factors such as drug side effects, other adverse events and costs of implementation the treatment of interest may not be seen as a visible alternative to the next best treatment.

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Ethical issues• In intervention trials ethical considerations are more important than

in any other type of epidemiological study. • Intervention trials are ethically justified only in a situation of

uncertainty, when there is genuine doubt concerning the value of a new intervention in terms of its benefits and risks. • The researcher must have some evidence that it may be of benefit,

for instance, from laboratory and animal studies, or from observational epidemiological studies.• Otherwise, there would be no justification for conducting a trial.

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• Before participants are recruited into atrial, it is important that they are

fully aware of what the study is about, what it is for and what the potential risks are. Participants then need to give their consent to participate. This is known as informed consent. • Sometimes it is not possible for the participant to provide their consent.

For example , if the intervention is a childhood vaccine, then the consent will need to be sought from the parent or guardian of the child; and if intervention is a drug that is hoped to improve the recovery of patients with severe head injuries , then it is likely that consent will be required from close relative or guardian. Whatever form of consent is obtained, it should always be clearly stated when the results of the trial are reported.

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• It also important that trial participants are allowed to refuse to

participate and have the option to drop out of the trial at any time during the study. As with any study, the identity of the trial participants should be kept confidential and their privacy respected.

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Strengths of field trial• Helpful in assessing the value of new strategy to prevent risk of a

certain diseases in developing countries.• Can evaluate a single variable in a precisely defined group of people.• Eliminates bias by comparing two otherwise identical groups• Able to control selection, confounding and measurement biases

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Weakness of field trial

• Major financial considerations• Think of how much work is required to randomize and allocate

participants to various treatment groups!• Ethical and practical limitations