Transversal study

A cross-sectional study (also, prevalence study or vertical study; cross-sectional study or cross sectional survey) is a statistical, demographic and epidemiological study, used in the social sciences and health sciences. This is a type of observational and descriptive study that measures both the prevalence of exposure and the effect in a population sample at a single point in time; that is, it allows estimating the magnitude and distribution of a disease at a given time. Cross-sectional studies, as opposed to longitudinal studies, confound age and cohort effects, and may not differentiate between age differences or differences in time of birth as the cause of a change.

Prevalence studies

Prevalence studies are frequently used and can be considered as:

1. Descriptive studies because the objective is not to evaluate a working hypothesis.
2. Observational or non-experimental studies because there is no manipulation of variables by the researcher.
3. Cross-sectional study because there is no continuity in the axis of time.

The goal of a cross-sectional study is to find out all the cases of people with a certain condition at a given time, regardless of how long they will have this disease or when they acquired it.

Technique of a cross-sectional study

1. Selection of a sample of study population.
2. Measurement of the predictor variable (risk factor) and outcome variable (fermity).

Usefulness of cross-sectional studies

Prevalence studies are frequently used in Public Health, because they allow:

1. The description of a health phenomenon.
2. Identification of the population frequency of a health phenomenon.
3. The generation of working hypothesis or explanatory hypothesis.

Advantages of a cross-sectional study

1. They allow to study several variables result as disease and exposure.
2. Good control of the selection of study subjects.
3. Little time of execution of the study since there is no follow-up of individuals and generally little economic cost.
4. They are a good initial step in preparing a cohort study.
5. They provide prevalence estimators.

Disadvantages of a cross-sectional study

1. Impossibility of determining whether the exposure precedes the disease, that is, impossibility to establish directionality of associations.
2. Exposure information is very vulnerable to measurement errors, especially if it is retrospectively collected. There is temporary ambiguity if present exhibitions are collected.
3. Impossibility of distinguishing between risk factors and prognostic factors because researchers know how many individuals have passed the disease.
4. Possible survival bias: The observed cases may have greater survival, since the deceased do not usually enter the study.
5. It is not effective to study rare, lethal or short-lived diseases.
6. Impossibility of identifying causal relationships between the factors studied, since it measures simultaneously effect (dependent variable) and exposure (independent variable).

Cross-sectional study versus longitudinal study

In longitudinal studies, measurements of the variables of a group are repeated over an extended period of time or on different occasions. The factor is time and the influence of its evolution on the facts.

Longitudinal versus cross-sectional studies differentiate between age and cohort effects.