Once you have decided that you want to perform a specific study after having analysed a particular public health problem, you will usually take the next step by writing a study protocol.

The Study Protocol is a document that describes every step of the study and answers relevant questions about topics such as the public health problem that will be addressed, the study questions that need to be answered, what objectives the study will achieve, how much power the study will have and what the impact of the findings will be on public health.

The purpose of writing a study protocol can include the objective to acquire funding or ethical approval for the study, to lay down the rules to all study partners or just to ensure that all study team members are on the same page in terms of expectations and contribution. 

A possible useful outline of your study protocol could be with the following chapters:

  1. Presentation
  2. Background and justifications
  3. Objectives
  4. Methods
  5. Ethical considerations
  6. Project management
  7. Timetable
  8. Resources
  9. References
  10. Appendices


The presentation includes the Formal Title of the study, with a  short, accurate and concise summary of what it is about. In this section all the investigators are presented as well as the main centres that collaborate in the study.

The Steering Committee (or scientific board), if present, will be mentioned here, as well as a summary of the protocol.

Background and justifications

This section includes the specific statement of the public health problem and the justification for this study. This will also describe what specific gaps in existing scientific knowledge this study will fill.
The importance of the subject area has to become evident after reading this part of the document, including the magnitude and frequency of the disease that is under investigation.
The description of the gaps in existing knowledge about this topic require a comprehensive and rigorous literature review, which will often benefit from the support of an experienced librarian or documentalist.
The principal questions to be addressed have to be described here as well as an indication how the expected results will contribute to existing knowledge. Describe how you plan the dissemination of results and more importantly, how policy makers or decision takers can use the results.


The objectives should answer the study question and need to be worded "S.M.A.R.T.". If there are more than 1 objectives, then it may be useful to distinguish between Principal objectives (that must be achieved and that dictate the design and methods of the study) and Secondary objectives (which may be of interest, but not essential).

The objectives then need to be translated to hypotheses in terms that allow statistical testing.

An example:
Non S.M.A.R.T objective: "To identify risk factors for HCV infection"

SMART objectives:
Principal objective: "To determine if sharing a haemodialysis machine with a HCV infected patient is a risk factor for HCV infection"
Secondary objective: "To identify failures in procedures designed to prevent cross-infection via haemodialysis machines"

Hypothesis: “The incidence of HCV infection in haemodialysis patients is higher in patients sharing machines with HCV infected patients than in patients not sharing machines with HCV infected patients”


The methods section describes in specific detail the procedures to achieve the study objectives: what will exactly be done and how? The information in this section will be used by decision makers and financing organisations to judge the validity of your proposal.
It includes the description of the Study Design (cohort, case control, cross-sectional…) plus a brief justification for the design choice.

Furthermore the Study Population is specified here:

  • definitions (population, exposures, outcomes) 
  • selection
  • criteria for inclusion and exclusion
  • mechanisms of recruitment
  • accessibility, follow-up, representativeness

Sampling design

Description of the sampling frame (district, household, persons,…), method (random, cluster, stratified,…), randomisation procedures, replacement procedures (in case of refusal) are described here.

Sample size and power calculations need to be specified here, which are based on the principal objective. This section will then also indicate the feasibility of performing a study of this size.

Example definitions:

Exposure is defined as: "consumption of custard slices in June or July 1991"
Case definition: "a person living in South-West Wales with a laboratory confirmed infection due to S. Enteritidis in June and July 1991"

Case finding takes place through: Public Health Laboratory; weekly notifications
Controls definition:  "persons living in SW Wales in same neighborhood as cases"
Control finding: random selection of people using telephone directory

Data analysis plan:

This part of the methods is structured in terms of objectives. For each of the hypotheses tested it includes dummy tables (clarifying the comparison of groups, which risk factors or protective measures are compared). If appropriate the assessment of dose-response relationship for key exposures and assessment of possible confounding factors / effect modifiers.

The plan includes a description of the statistical tests used and what type of adjustment is made to the analysis (e.g. stratification, multivariable analysis)

Define the indicators you will need to reach objectives and specifically what data you will need to collect.

Data collection

Describe how data will be collected (interview, observation, record review) and by whom (interviewers? in that case describe selection, training and level of supervision). What will be the tools for data collection (questionnaires, recording materials). In case questionnaires are used: will they be self or interviewer administered, face-to-face or telephone interviews?

To check appropriateness of your data collection instrument use the practical guide.
Describe if data collection will be blinded or not and the procedures for taking samples.

Data handling:

How will coding of the data take place (e.g. anonymisation)? During data collection or afterwards? And by whom?
What will be the procedures for data processing (what software and hardware used, method of data entry). Will data entry be done during the data collection or afterwards? Will it be single or double entry?
What will be the steps for validation and data cleaning?

Pilot studies and pre-testing:

Some investigators say that "No study should be done without a pre-test". Such a test helps to assess the feasibility of sampling, check if data collection plans are realistic. It tests the measurement methods and questionnaires.

Describe how you will perform the test.


A relevant part of the methods section in your study protocol is the identification of potential sources of biases (e.g. selection bias, information bias, misclassification bias, interviewer bias).

How to deal with them? Will you consider possibilities for correcting? How will these limitations affect the results?

Ethical considerations

In this section, all ethical considerations of performing the study are to be discussed. An obvious start is to ensure that the participants have a good understanding of what participating to the study well mean for them personally: will they have to supply confidential information? If yes, how will these data be protected? How long will the data be stored? Will their names and personal details remain attached to the data?

Will participants be expected to be subject to laboratory investigations? If so, will they be informed about their individual results?

All these questions need to be clarified in this section, and explained how participants are informed about these procedures, and how they will be asked to give their "Informed consent".

If required, this information needs to be translated in the local (lay) language.

Most countries require population studies to be approved by an Ethics committee: in that case a section such as this will need to address all their possible questions.

Project management

Use this section to describe in detail the participating institutes and persons, in order to acknowledge in advance their contribution and role. Describe clearly enough the responsibilities and tasks of each partner.

Who will have access to what data? How is data ownership documented and agreed upon. Use also this paragraph to describe in advance the distribution of roles for authorship. The Vancouver criteria will be helpful here (see reference section below)


All operational and practical issues can be described here, including planning- and organisation of the study, when milestones will be finished such as questionnaire design, recruitment of participants, purchases of materials.
If permissions are required (e.g. to include certain staff in your project team, to spend certain funds or to contact the study population) then here you need to include a timetable with deadlines for each of these permissions
When funding need to be obtained, indicate here the deadlines for having approval for those funds. 

Pilot study
time to do adjustments

Final study
data collection
presentation of results and write up


Extent of this section depends on target audience
available sources
requested sources
Keep budget
well justified


 Limit number of references to key articles
Follow recommended style



Methodological appendices
List of definitions
Introductory letters to study participants
Informed consent forms

See also the following EPIET Lectures:

Writing a Study Protocol