Epidemiology and Biostatistics Questions and Answers

Answer: A

The primary aim of epidemiology is to describe the distribution and magnitude of health and disease.

Epidemiology studies how health-related states are distributed in populations and what determines them. Its first aim is to describe the size of health problems and their distribution by time, place and person, which then lets it identify causes and guide control measures.

Measuring mortality is only one of its tools. Health education is an application of its findings, and treating disease is the work of clinical medicine, not epidemiology.

Answer: D

The one that is not a study design is Incidence study.

Incidence is a measure: the number of new cases of a disease in a population over a period. It is calculated from studies but is not itself a type of study.

The other three are standard epidemiological designs. A cohort study follows exposed and unexposed groups forward to see who develops disease. A case control study starts from people with and without a disease and looks back at past exposures. A cross-sectional study measures exposure and disease at one point in time.

Answer: C

The child mortality rate is the total number of child deaths under the age of five years per 1000 live births.

Child mortality, also called the under-five mortality rate, measures the probability of a child dying before the fifth birthday, expressed per 1,000 live births. It is one of the main indicators of child health and was a target of the Millennium and Sustainable Development Goals.

The age limit is five years, not two, and the rate is expressed per 1,000, not per 100, which rules out the other three options.

Answer: C

Years of life lost through premature death plus years lived with disability, adjusted for severity, are known as disability adjusted life years (DALY).

One DALY is one lost year of healthy life. It is the sum of the years of life lost (YLL) and the years lived with disability (YLD), the latter weighted by the severity of the disability.

The Human Development Index combines income, education and life expectancy. Health adjusted life expectancy (HALE) is the expected years of life in full health. Sullivan's index is a life expectancy corrected for disability, so it is not a count of years lost.

Answer: B

The statement that the tenth revision of the ICD took place in 1995 is incorrect.

The tenth revision of the International Classification of Diseases was approved by the World Health Assembly in 1990, and countries began to use it in the mid-1990s, so 1995 is not the date of the revision. It has 21 chapters and is the standard for comparing morbidity and mortality internationally, and the classification has been revised roughly every ten years.

So the statements on 21 chapters, on the revision about every ten years and on the use as the international standard are the accepted ones, and the one giving 1995 is the incorrect one.

Answer: D

If a drug prevents death but does not cure, prevalence will increase.

Prevalence depends on incidence and on the average duration of the disease. A drug that keeps patients alive without curing them lengthens the time they live with the disease, while the number of new cases is not affected. The pool of existing cases therefore grows.

Incidence counts only new cases, so the drug has no effect on it, and the options that say incidence will decrease or increase are wrong. Prevalence would fall if the drug cured patients or if they died sooner.

Answer: B

Seasonal variation of a disease is assessed by comparing the incidence of the disease.

Incidence is the number of new cases in a period. Comparing the monthly or weekly incidence over the seasons shows when new cases rise and fall, as with malaria in the rains or influenza in winter.

Prevalence is the number of existing cases and changes slowly because it includes old cases. The survival rate and mortality rate describe outcome of the disease and not its occurrence over time.

Answer: C

Verbal autopsy assigns the cause of death by interviewing family members, is used where medical certification is not available, and uses a standard structured questionnaire, statements I, III and IV.

It is a method for finding the probable cause of death in areas where deaths occur at home and are not certified by a doctor, as in rural India. A trained interviewer questions the relatives about the symptoms before death with a set questionnaire.

Statement II is wrong, because no examination of the body is involved at all, and the whole point of the method is to do without a post-mortem.

Answer: B

In cross-sectional studies follow up is not needed, all cases are seen at one point of time, and chronic diseases are studied, statements I, II and III.

A cross-sectional study takes a snapshot of a population at one time, so no follow up is needed. It suits chronic conditions, whose prevalence can be measured, as with hypertension or diabetes.

Statement IV is wrong: because exposure and disease are measured at the same time, the study cannot show which came first, so it cannot establish a cause and effect relationship. It can only suggest hypotheses.

Answer: B

In cross over studies statements I, II and IV are correct.

In a cross-over trial each subject receives both treatments, one after the other, so all subjects get the therapy of interest. The design is not suitable if the therapy cures the disease, because the patient cannot then serve as a control for the second treatment, and it is not suitable if the therapy acts only at a certain stage of the disease.

Statement III is wrong: the design needs a stable disease, since if the condition changes radically during the study, the two periods are not comparable. That is why the options containing III are rejected.