How does the publication cycle work?

What is the publication cycle?

The publication cycle is an inseparable and critical aspect that every researcher or writer needs to understand. This is because the publication cycle gives a tangible form to a theoretical concept, an idea, or an expression of writing talent. To use a commercial term, it is much like an assembly line where an idea passes through various inter-related processes and iterations before it develops into its final published form.

Content and medium: Two determinants of the publication cycle

The publication cycle differs based on two factors: the nature of content and the medium of publication. A writing output can belong to one of a myriad range of topics and publication mediums.  Some writers present their ideas in the form of research articles on various topics in, inter alia, journals, dissertations, conference papers, and scholarly books. Conversely, the output of other writers might be in the form of informal writings that appear in magazines catering to the general reader.

Apart from the nature of content, publications also differ in the medium selected for publication. Unlike most of the 20th century, publications are no longer limited to the print medium. In fact, the digital revolution and advent of the Internet have given an entirely new dimension to publishing with the popularity of articles and even books published on the web and in the electronic medium. Therefore, one needs to understand that the publication cycle, or the intervening processes for an idea to reach the reader, is determined by several factors. These factors determine the processes and the time cycle for a writing to be published in its final form.

Electronic publications include two categories. The first is the category of online publications on the World Wide Web. These include personal web pages of the author, individual blogs, online videos or presentations, as well as online research journals or periodicals. The second category includes electronic books, often referred to as e-books, which are bought and sold in the market, but the reader can access them only by using software on a digital device or a personal computer.

Conversely, the more conventional publications in print include research papers or reports published in journals, magazines, and books.

What does the publication cycle involve?

The publication cycle starts with the generation of an idea by the author or writer. This first step toward publication is basically an individualistic approach in the sense that it is a creative process and not a time-bound phenomenon.

After an idea takes root in the writer’s mind, the next step is to undertake the research that will help develop that idea into a well-constructed piece of writing. In this step, the authors search for existing literature on the relevant subject and identify the lacunae in such writing. This helps them make a useful contribution to their area of research.

The research work is followed by an informal communication among the authors (in case of multiple authors) that includes regular conversations on the phone and meetings for discussion of their research output. This stage provides a common platform for different authors to share ideas and views on a particular topic or idea of research.

The next major step involves report research. This could either be an informal approach adopted by the author or authors to share their research on their individual blogs or web pages, or a formal approach that includes white paper publications, report publications such as lab or research reports, and presentations at conferences and colloquia.

The next step is to report the findings as a publication in journals and/or magazines. Such publications provide a platform for popularization of the authors’ work, or to bring the research to the notice of a wider readership.

The culminating point of the publication cycle of a research idea occurs in a book or encyclopedia publication.  This is the most formalized medium of publishing a research work, and is recognized as the ultimate achievement for a researcher.

Each stage of the publication cycle is relevant because it constitutes a step in the ladder toward the final form of a research idea. Considered holistically, an understanding of the publication cycle facilitates the development of an efficient strategy for publication of a research work in an organized manner.

Conference papers vs journal publications: Which is the better publication route?

In course of their research, academicians often need to interact and exchange views with their colleagues to provide a firmer ground for their inferences. Such meetings help them debate their research topic with other like-minded participants and then assimilate the information that is presented through audio-visual media to produce a more conclusive finding. Therefore, seminars and colloquia are an essential part in the growth of any research. Often the proceedings of such meetings are recorded in the form of a collection of papers that were presented during the event.

On the other hand, a journal publishes research work, either on the web or as printed copies, after a rigorous process of review and a long approval cycle. However, once published in a reputed journal, your paper has an audience that you would otherwise have never had access to.

Why opt for conferences?

Conference proceedings have several advantages for a researcher. This is because conferences:

– Give a platform for interaction among research scholars who share a common interest.

– Have a faster review process and generate a faster feedback.

– Are often characterized by short presentations, so they manage to present the aim of the research clearly without consuming too much time.

– Include discussions sessions, which encourages exchange of views and ideas on the presentations.

– Allow interaction of scholars from all over the world who are engaged in the same or allied research fields.

– Have a predictable and time-bound review time.

– Help the presentations to be properly archived for reference in similar events held elsewhere on related research topics.

– Involve sponsors, who allure researchers with publishing credits and personal and professional benefits for attending the conference.

– Have high visibility and often leave a greater impact on the academic fraternity.

– Mainly focus on recent researches or up-to-date academic endeavors, unlike a journal that often takes a long time to finally publish a research.

Demerits of a conference publication

On the flip side, conferences have the following drawbacks:

– The review process is often superficial or cursory, i.e., there is no second round of reviewing.

– They have a low acceptance rate.

– The feedback from the research fraternity may be lukewarm compared to a publication in a journal.

– Economies of scale work against good quality publications because the publication is one of many expense heads for the organizers. Therefore, the production quality often leaves much to be desired.

Why opt for a journal publication?

A publication in a reputed journal presents the following advantages for the researcher:

– Research papers that are published in journals are thoroughly peer reviewed, including multiple review phases.

– The quality of research published in a journal is of a high standard.

– Journal publications carry deep analysis of a research work.

– Useful feedback is received from the reviewers, which help bring about substantive changes in the paper to improve the research analysis.

– Word and page limits are longer in the case of journals. This gives more scope to the researcher to express his or her thoughts and interpretations.

– A journal gives a chance to authors to revise their work based on the feedback and then re-submit it for further review and publication.

– Conference papers are never considered the ultimate in publishing a research. Often, conference papers can be converted to journal papers and published in reputed journals with a high impact factor.

Demerits of journal publications

There are also few demerits of journal publications. These include:

– The publication process is time-consuming.

– Due to such delays, the research topic might get outdated.

– Selection of journals is a difficult task. Sometimes, a good research is published in a sub-standard journal.

Both these routes to publication have their pros and cons. It must also be noted that conference proceedings and journal publications are not mutually exclusive; a situation may arise where one form of a research work might be published in the conference proceedings and another, perhaps more developed, form might be published in a journal. Therefore, for a more diverse and in-depth research output, both conference proceedings and journal publications need to play a significant part.

Conflict of Interest Disclosure

A fundamental requisite of a publication in any reputed journal is the need to provide readers with unbiased and unambiguous research. Toward this objective, a published article should disclose whether the author or authors had any competing interest or conflict of interest while preparing the article. Consequently, the onus is on the journal to publish such disclosures in the paper so that readers, who include researchers, professionals, practitioners and scholars, are aware of them while evaluating the paper.

According to the International Committee of Medical Journal Editors (ICMJE), there is a case of “competing interest” or “conflict of interest” when professional judgment concerning a primary interest (such as patients’ welfare or the validity of research) may be influenced by a secondary interest (such as financial gain). Such conflict is likely to affect the credibility of the journal as well as that of the author(s).

Conflict of interest may arise from potential relationships or allegiances, or from hostilities against particular groups or organizations. It may occur when a specific factor influences one’s judgments or actions significantly. In such situations, personal gain has an ascendancy over scholarly output.

Today, most journals publish papers that are not only based on the output of the authors, but also largely impacted by the inputs of peer reviewers, editors, and editorial board members of the journals. All such participants, who play a critical role in the process of finalizing a paper for publication, also need to seek any disclosure from the authors that could be perceived as a potential conflict of interest.

The general format of the conflict of interest form includes:

  • Author and co-authors’ conflict of interest.
  • Statements declaring whether the supporting sources are involved in the study design, collection, analysis and interpretation of data.
  • Explanation regarding the authors’ access to the study data, including the nature and extent of the authors’ access and validity.

Declaration of any conflict of interest is an ethical requirement for researchers at the time of submitting their manuscripts for publication. Being upfront about any potential conflict of interest is likely to increase the trust of the readers in the publication and places them in a position to make an honest evaluation of any likely bias in the research findings.

Retraction of Publications

Your published articles give you recognition as a writer and boost your academic credentials. However, there are special circumstances when an article might be withdrawn or cancelled even after its publication. This process is called retraction of publications.

Research articles go through a review process prior to publication. However, there are occasions when major errors are detected in a research paper after it is published. In such circumstances, the journal is forced to issue a retraction notice to withdraw the publication. Retraction enables journals to alert or inform readers about the errors in the findings or conclusions of the paper. Some journals, however, retract papers without citing specific reasons because they fear a loss of credibility in the journal. In recent months, there is a discernible increase in the retraction rate in the publication industry.

According to the Committee on Publication Ethics (COPE), publications can be retracted by journal editors if:

  • They have clear evidence that the findings are unreliable, either as a result of misconduct (e.g., data fabrication) or honest error (e.g., miscalculation or experimental error).
  • The findings have previously been published elsewhere without proper cross-referencing, permission or justification (i.e., cases of redundant publication).
  • It constitutes plagiarism.
  • It reports unethical research.

Even though retraction of a publication is the decision of the journal’s editor, sometimes the author of the paper may also be asked by the editor to formally issue the retraction. In some journals, both the editor and the author issue the retraction notice. Nevertheless, the journal’s editor can retract the published paper unilaterally in case the author refuses to do so.

The retraction notice should cite the reasons for the retraction and clarify whether the retraction is for misconduct or for honest and genuine mistakes. The notice also needs to mention whether the publication is being retracted by the editor or the author. Retracted publications should not be removed either from online or printed copies of the journal; instead, the status of the retraction should be clearly indicated in the publication.

Retraction of publications is likely to have an adverse impact on the credentials of both the author and the journal. Therefore, it is important to take precautionary measures to avoid such a scenario.

Transgenic Approach for Value Addition

Transgene: It is considered to be a gene or a genetic material of interest that is transferred from one organism to another, either naturally or by artificial transformation methods.

Methods involved in transgenics:

Transformation techniques: The transformational methods can be of different types, i.e., direct or indirect.

Some of the widely used direct transformation methods are microinjection, electron gun, electroporation (physical methods); calcium phosphate method, liposome-mediated transfer method (chemical methods), etc.

Indirect transformation methods are also known as vector-mediated gene transfer methods. The major biological vectors involved are Agrobacterium tumefaciens, viruses (for e.g., CaMV virus), etc.

Genome editing: As the name suggests, part of a genome is edited, i.e., either any sequence is inserted, or deleted or replaced by any other desired sequence, with the help of restriction enzymes (also termed as molecular scissors).

Value addition properties of the transgenic process:

  • It has ensured enhanced yields to the farming community, in quantitative terms, by introducing various superior crop varieties, that upholds various high performance qualities like insect or pest resistance, herbicide resistance, resistance to various other biotic stresses, as well as resistance to various abiotic stresses like drought, salinity, flood, temperature imbalance, etc.
  • The above resistance in the crops has also led to an improvement in the crop quality.
  • Transgenics have been a boon, not only in the field of agriculture, but also in other fields like aquaculture, sericulture, horticulture, etc., through an increase in the productivity and quality of the resembled products.
  • Transgenics have opened up the world market for various commercial products obtained through genetic manipulation. For e.g., Flavr Savr tomato, the first ever genetically engineered crop product to be marketed and commercialized by a California-based company, Calgene, which succeeded in introducing an antisense gene that interfered in the production of the fruit ripening enzyme (Polygalacturonase enzyme).
  • One of the landmark achievements of the transgenic technique was the introduction of the gene therapy. The technique aimed at treating a disease in a patient, those who experienced low concentration of any of the metabolically important protein or enzyme production. The introduced gene in the patient leads to altered functions of the genetic material, but in a productive way, only in relation to the disease.
  • Transgenic methodology has brought about a revolutionary change in the field of medical science by prologue of various therapeutic methods, which involve the development of modern vaccination techniques, new and more efficient vaccines for various untreated diseases, production of antibodies from various biological vectors (microorganisms as well as plants), production of monoclonal antibodies by hybridoma technology, and the production of certain other important drugs used in treating genetic diseases.
  • The field of transgenics has been considered important for the researchers and scientists, giving them an ample opportunity for creating substantive and commercially important products, which would meet the demands of the overgrowing world population.

Apart from all these advantages, the mounting costs of the products are making it less appealing, for both the researchers and the customers who tend to buy it. Even certain ethical issues, related to the genetically engineered food products are preventing its market exposure and availability.

Importance of Statistical Review of manuscripts

Statistics: It is a branch of mathematics that deals with the collection of data, its analysis, interpretation, presentation and sequential organization. In simple terms, it deals with philosophy, logic, and expression of data.

Who does the statistical review?

Statistical review is basically done by the expert statisticians or authors and journal editors with statistical knowledge. It comprises of statistical and even methodological questions that are to be answered by the author or even the journal editors that are put forward by the reviewer.

Role of the statistical reviewers:

  • The statistical reviewers find out the possible statistical error sources in the manuscript, in turn increasing the statistical accuracy of the paper as well as ensuring quicker publication of the manuscript.
  • All forms of statistical data checking is performed by the statistical reviewers like checking the missing data, checking whether correct statistical methods were followed or not, checking whether the statistical methods were used appropriately or not, checking for statistical errors like error in level of significance during analysis of the data, checking whether appropriate name of the statistical package is mentioned or not along with the version used, checking whether the measurable units are properly mentioned or not, checking whether the tables and figures displayed in the manuscript hold a proper self-explanatory footnote or not, and so on.
  • They ensure proper statistical presentation of data throughout the manuscript; proper use of statistical language is also ensured by the reviewer in the data presentation section.
  • The reviewer also checks whether the conclusion section in the manuscript is justified or not with regard to the presented data.
  • They also cross check the feasibility of the discussion section based on the results.

Significance of statistical review:

  • If there is any kind of major statistical errors found in the data presentation section, then it may lead to the rejection of the research paper. So, reviewing of the statistical data and its proper presentation is of utmost importance for the author. The frequent statistical problems in the manuscript are found in data interpretation and presentation, its analysis and the study design.
  • Sound statistics is the foundation to high-quality research work interpreting quantitative studies.

Gift authorship: A provocative issue

Assigning authorship for the real contributors can be a tricky business for the scientific or the academic writers.

What is gift authorship? In simple terms, it is defined as the co-authorship, conferred to those having a little or no intellectual contribution in the study. Gift authorship provides just an authority stamp for the non-contributors.

Authorship criteria: The person affiliated under this type of authorship, do not meet the authorship criteria defined by various international bodies. According to one of the giant international body, known as International Committee of Medical Journal Editors (ICMJE), authorship criteria are stated as follows:

(i) Substantial contributions to conception and design, acquisition or collection, analysis and interpretation of data;

(ii) Drafting or revising the article, critically for important intellectual content; and

(iii) Giving the final approval of the edited version of the article, to be published.

Ethical viewpoint of gift authorship: Gift authorship is regarded as highly unethical and irrelevant, as the author honored with the title of authorship holds no contributing hands, neither in the designing nor in data analysis; he/she do not meet the authorship criteria. He/she may not have expertise in the field to which the study is related, which may bring dismay to the institute or the publishing journal. This kind of authorship has cropped up in an intense way in the medical writing field, demanding an immediate action to be taken against this illegal authorship, as this dilutes the credentials of the authors who have done the real work, related to the study protocol.

Reasons for researchers opting for gift authorship: There are many identified reasons that put the precocious researchers to opt for the option of gift authorship.  Some of the most cited reasons are:

(i) Superiority complex of the guide or the lead supervisor. They do not allow any research article publication by their junior counterparts; and

(ii) Certain researchers believe that assigning the names of their head supervisor or institutional head can lead to increased readability and help in publication of their articles.

The researchers should think of undermining such authorship that leads to the loss in the credibility of the real contributing authors and diluting their work profile.

Is self-plagiarism ethical?

Research papers or journals are the medium of spreading knowledge and new ideas evolved. Innovative and original piece of work would certainly be more educative and admirable. Nevertheless, authors and writers are often found to be reusing their old piece of work or some extracts from their previous published papers while writing a new research paper.

When questions are raised against this content reuse, authors claim that those stuffs are their own works and materials, and thus, they can reuse them as they wish, and it cannot be termed as plagiarism since they have not stolen the ideas from any other author or source.

The ethics of plagiarism are not applicable to such reuse, as a result of which it has been overlooked till date. While the discussion is whether this reuse is ethical or not, the publications and the journals, on the other hand, have set certain guidelines for such works citing it as Self-plagiarism.

What is self-plagiarism?

Self-plagiarism is a form of plagiarism where the writer reuses his/her own previously published work in portions or entirely while creating a new study paper. It can breach the publisher’s copyright on those published work when it is reused in the new study papers without appropriate citations. Let us now know more about the ethical aspects of self-plagiarism.

Self-plagiarism can be detected when:

a)  A published paper is used to republish elsewhere without the consent of the co-authors and the publisher of the paper or work.

b)  A paper of a large study is published in small sections with an intention to increase the number of publications.

c)  A previously written work either published or not is reused again in portions in the new study papers.

Although the laws of self-plagiarism are not enforced, it somehow reflects the dishonesty of the author. Moreover, the journals and the publishers are rejecting such copy-paste works as they are seeking writings based on original research findings and proper citations of all the references.

Nowadays, journals are also pointing out questions on the reuse of one’s own work. In order to avoid self-plagiarism, one should try to keep his/her work original, and in case it is necessary to include any portion from his/her previous works, it should be then properly cited with proper references. I hope this article will surely help you in detecting prospective self-plagiarism before submitting your paper or work to publications or journals.

Analytical Study Design in Medical Research: Cohort study

Cohort studies are observational analytical studies. As mentioned in my previous blog (http://blog.manuscriptedit.com/2014/02/overview-different-analytical-study-designs-medical-research/), the word ‘cohort’ is derived from the Latin word ‘cohors’, which means unit. For conducting cohort type of studies, the study population is chosen from general population both exposed to a certain agent suspected for disease development and unexposed to the cause. The population is followed for a longer period of time. The incidence in disease development in exposed group is compared with the non-exposed group. Therefore, the objective of a cohort study is to find out association between a suspected cause(s) and disease. If performed correctly, cohort studies can predict results comparable to the experimental analytical studies. The following measurements can be done in a cohort study design: absolute risk or incidence, relative risk (risk ratio or rate ratio), risk difference, and attributable proportion. Cohort studies are classified as prospective and retrospective studies based on the timing of enrollment of subjects and disease outcome.

Analytical Study III_Fig1


Prospective Cohort Study

As the name suggested, prospective cohort studies are started with a population containing non-diseased subjects but all having a risk to develop a certain disease, and the investigator waits for the disease to develop. The population is divided into two groups, one with the exposure of the potent agent or environment suspected to be associated with the disease, and the other remains unexposed but with equal susceptibility to develop the disease. Then the population is followed up for a certain period of time until they develop the condition or disease. After following up the study population for a certain period of time until the disease developed, the incidences of disease in exposed and unexposed population are calculated (see the following schematic diagram). Therefore, incidence rate is the measure of disease in cohort studies. The association to disease is measured by relative risk (RR).

           Analyt Stydy III_Fig2a (1)Analyt Stydy III_Fig2b

From the above table, the incidences of disease in exposed and unexposed population, relative risk (RR) can be calculated.

Analytical Study

Alternatively, odd ratio (OR) can also be a measurement of association and is the ratio of two odds. Again, we can obtain odds from the ratio of chances of something to happen to that of not happening. In this case, the OR can be calculated as follows:

 

OR = a/b : c/d

 

Attributable risk or exposure attributed to the disease in total population or in other words population attributable risk (PAR) can also be calculated with respect to the total population.

The Framingham heart study is a good example of this type of prospective study. Started in 1948, this study is still going on. The Framingham heart study was undertaken to determine common contributing factors to cardiovascular disease. The Framingham risk score based on the Framingham study can predict 10-years cardiovascular risk in an individual with no known cardiovascular disease.

Advantages of prospective cohort study include the following:

(i)                 Better for rare exposure

(ii)               One can determine the disease incidence rate and relative risk

(iii)             More than one disease associated with a single exposure can be determined

(iv)             This study is able to establish the cause-effect

(v)               Selection and information biases are minimized

However, the study has certain limitations as well. The study requires a large population and long time to complete. Loss of subjects in long time follow-up adversely affects the outcome of the study. Prospective study is insufficient in rare diseases. Moreover, this type of study is expensive and has ethical issue too.

 

Retrospective Cohort study

Retrospective cohort study, also known as historical cohort study, is a type of cohort study where data are collected in past, but analyzed at present (see the inset diagram). Here, the investigator retrospectively Analytical Study identifies the exposure and the outcome information. A retrospective study design is chosen for a rare or unusual exposure for which a prospective study design will not be appropriate. In addition, retrospective study design can quickly estimate the effect of exposure on certain outcome as well as determine the disease association. This type of study is helpful in designing future studies and interventions. The data are collected from past medical records, administrative databases, conducting patients’ interviews, etc. Odd ratio is used as the measure of association between the exposure or risk factor and disease. The other measurements are same as prospective cohort study.

A classic example of retrospective study is the study conducted by Case et al (1954) to examine the excess risk of bladder cancer in men worked in the manufacturing plant of certain dye intermediate. In this study, the authors first made a list of men who worked in chemical plant manufacturing dye in UK at least six months since 1920. The investigators searched retrospectively for the cases of bladder cancer among those workers who had been employed in dye manufacturing chemical plants between 1921 to till February 1952. The number of cases of bladder cancer among these workers was then compared with the number of bladder cancer incidences in general population to determine the excess risk of bladder cancer in men exposed to certain dye intermediate.

Advantages of retrospective cohort study include the following:

(i)                 Good for rare exposure

(ii)               Unlike prospective study, this study takes relatively short time to complete

(iii)             Relatively less expensive

(iv)             Can be conducted for multiple cohort

(v)               Estimate the incidence data

(vi)             No ethical issues involve

 

However, retrospective cohort study design has certain disadvantages, especially, the chances of selection bias in sampling is relatively higher. Sometimes it may be difficult to identify the appropriate exposed group and corresponding control group or the group for comparison. Confounding is another issue in historical study design; loss of follow up may also bias the study results. In addition, like prospective cohort study, retrospective cohort study is not appropriate for rare diseases. Poor quality of available medical data not designed for such study often adds error in results.

 

References

1. Morabia, A (2004). A History of Epidemiologic Methods and Concepts. Birkhaeuser Verlag;  Basel: p. 1-405.

2. John-Hopkins open courseware.

http://ocw.jhsph.edu/courses/fundepiii/lectureNotes.cfm

3. Emily L. Harris EL. Linking Exposures and Endpoints: Measures of Association and Risk

http://www.genome.gov/pages/about/od/opg/epidemiologyforresearchers/3_harris.pdf

4. Framingham heart study, a project of the National Heart, Lung, and Blood Institute and Boston University. http://www.framinghamheartstudy.org/fhs-bibliography/index.php

5. http://www.iarc.fr/en/publications/pdfs-online/epi/cancerepi/CancerEpi-8.pdf

6. Case RAM, Hosker ME, McDonald DB, Pearson JT (1954). Tumors of the urinary bladder in workmen engaged in the manufacture and use of certain dyestuff intermediates in the British chemical industry. Part I. The role of aniline, benzidine, alpha-naphthylamine, and beta-naphthylamine. BR J Ind Med 11:75-104.

Analytical Study Design in Medical Research: Measures of risk and disease association

A researcher, while designing any analytical study in medical research, should be aware of few basic terms in epidemiology required to measure disease risk and association. This blog article focuses on defining those terms used for calculating disease risk and association. As mentioned above, there are two different types of measurements: Measures of risk and Measures of association.

Measures of Risk

Risk is defined as the probability of an individual developing a condition or disease over a period of time.

Risk = Chances of something to happen/ Chances of all things to happen

Odds= Chances of something to happen/ Chances of it not happening

Therefore, “Risk” is a proportion, while “Odds” is a ratio.

Incidence: Incidence is a measure of risk which describes the number of cases developed a new condition for a specified period of time. In this context, there is another important term, “Incidence proportion” to be worth mentioning. It is defined as the proportion of the number of cases developed a new condition and total population including the cases with developed condition and no condition in a specified period of time.

For example, among 100 non-diseased persons initially at risk, 20 develop a disease/condition over a period of five years.

Incidence = 20 cases

Incidence proportion = 20 cases per 100 persons i.e., 5%

Incidence rate = 20 cases developed in 100 persons in 5 year means the rate of incidence is equal to 4 per 100 person-years

Prevalence: Prevalence is the proportion of the number of people having a condition at a specific point of time and total population studied. This is specifically called point prevalence. For example, at a certain date, five persons are detected having a condition among 100 people studied. There are two more terms need to be defined in this regard: Period prevalence and Life time prevalence (LTF). The former is defined as the proportion of the number of people having the disease at a certain period of time, say a month or period or a year and the total population studied at that period of time. On the other hand, LTF is defined as the proportion of the number of people having the disease at some point of their life and total population studied.

There is a very subtle difference between incidence and prevalence. Incidence is the frequency of a new event, while prevalence is the frequency of an existing event.

Cumulative Risk: Cumulative risk is defined by the probability of developing a condition over a period of time.

Measures of Association

Association is defined as a statistical measurement between two or more variables.

For measuring the strength of association of a disease for etiological and hypothesis testing, following measurements are important. The terms defined below are used to measure the association between exposure and disease.

Relative risk (RR): The relative risk is measured as a ratio of two risks.

For example, in 100 people consisting of 50 male and 50 female, while 20 male are infected with Tuberculosis, 10 female develop the condition.

Risk in men: 20/50

Risk in women: 10/50

Therefore, relative risk (RR) of developing Tuberculosis in men compared to women is

RR = 20/50 : 10/50 = 2.0

i.e., men are at double risk of developing Tuberculosis as compared to women.

Odd ratio (OR): Odd ratio is measured as the ratio of two odds (odds is defined above).

Continuing the previous example of Tuberculosis in men and women in a total population of 100

Odds in men: 20/30

Odds in women: 10/40

Odd ratio (OR) = 20/30 : 10/40 = 2.67

Therefore, the odds of men getting infected with Tuberculosis are 2.6 times as high as the women developing Tuberculosis.

To measure the impact of   the disease association on public health, following measuerments are important. All these measurements assume that the association between exposure and disease is causal.

Attributable risk (AR): Amount of disease attributed to the exposure i.e., the difference between the incidence of disease in the exposed group (Ie) and the incidence of disease in the unexposed group (Iue).

AR = Ie – Iue

Attributable (risk) fraction (ARF): ARF is the proportion of disease in the exposed population whose disease can be attributed to the exposure.

ARF = Ie – Iue / Ie

Population attributable risk (PAR): The incidence of disease in total population (Ip) that can be attributed to the exposure.

PAR = Ip – Iue

Population attributable (risk) fraction (PARF): PARF is the proportion of the disease in the total population whose disease can be attributed to the exposure.

PARF = Ip – Iue / Ip

 

Bias and Confounding Factors

In an epidemiological study, when association is found between exposure and disease, it is very important to check first whether the association is real. One needs to be cautious if the association is by chance due to non-adequate sample size or it is because of some kind of bias in the design or measurement.

Bias is a systematic error in design, conduct or analysis which results in unreal association of exposure with disease. There are three types of biases possible: (i) Selection bias, (ii) Information bias, and (iii) Confounding.

Selection bias occurs when selection of participants in one group shows different outcome in the selection of other groups. Information bias happens when information is taken differently from two groups.

Confounding occurs when the observed result between exposure and disease differs from the truth due to the influence of a third variable which has not been considered for analysis. For example, a person suffers from headache when he is under stress; however the person eats a lot of junk food especially, when he is in under stress. Therefore, it is hard to predict what actually causes the headache; whether it is lack of sleep, anxiety, gas formation due to indigestion. Therefore, all these variables should be adjusted before associating mental stress with headache.

 

References

1. Health Statistics New South Wales – Definitions. (n.d.). http://www.healthstats.nsw.gov.au/ContentText/Display/Definitions

2. SOURCES OF EPIDEMIOLOGIC DATA – KSU. (n.d.).

http://faculty.ksu.edu.sa/71640/Publications/COURSES/epidemiology-334%20CHS%20%20(70).doc

3. John-Hopkins open courseware. http://ocw.jhsph.edu/courses/fundepiii/lectureNotes.cfm

4. Manuel Bayona M, Chris Olsen, C. Measures in Epidemiology. In The Young Epidemiology Scholars Program (YES)

www.collegeboard.com/prod_downloads/yes/4297_MODULE_09.pdf‎

5. Emily L. Harris EL. Linking Exposures and Endpoints: Measures of Association and Risk

http://www.genome.gov/pages/about/od/opg/epidemiologyforresearchers/3_harris.pdf