PRIMARY RESEARCH

Descriptive studies

Observe and describe the behavior of subjects and patterns of outcome occurrence.

No Control group, Not Repeatable.

 Case series

 Case reports

 Cross-sectional studies

Analytical studies

Measure the association between exposure and outcome.

 Cross-sectional studies

 Cohort studies

 Case control studies

 Ecological studies

Cross-sectional study

A type of study that measures the exposure and outcome in a population at a single time point (A snapshot of a population). Begins by selecting a sample population and then obtaining data to classify all individuals in the sample as either having or not having the health outcome.

Aim

 Describe population characters

 Prevalence

 Hypothesis generation

Types

 Descriptive survey study: Describe the characteristics of a population or phenomenon being studied.

 Repetitive survey study: Asking the same questions at different times points to new sample people on each occasion.

 Longitudinal survey study: Asking or interviewing the same population at different time points, and to study rapid fluctuations in behaviors, thoughts, and emotions.

Advantages

 Inexpensive

 Short duration (no follow-up)

 More representative than case series and case reports.

Disadvantages

 Unsuitable for diseases of short duration

 Unsuitable for rare diseases.

 Bias

 Not possible to know if the outcome followed the exposure or if the exposure followed the outcome.

Cohort studies

What’s a cohort?

A cohort is a group of persons, usually 100 or more in size, who share common characteristics e.g. smokers, or people born in the same year.

What’s a cohort study?

A study of two groups which, a group of people are exposed to a particular risk factor and a control group that is not exposed. The two groups are free of the outcome and both are followed up for a duration of time to determine the different rates of outcomes.

Types

 Prospective cohort

At the time that the investigators begin enrolling subjects and collecting baseline exposure information, none of the subjects have developed any of the outcomes of interest. Then, follow up of subjects to determine changes in a certain outcome.

 Retrospective cohort

Retrospective studies are conducted after some people have already developed the outcomes of interest, yet the investigation starts from the exposure towards outcome as usual.

Advantages over prospective cohort:

Inexpensive

Less time consuming

 Retro-prospective cohort

A combination of the two types

The study starts in the past and continues in the future.

Advantage

 Can study multiple outcomes of the same exposure

 Good for rare exposure

 Eliminate recall bias.

 Well-defined relationship between an exposure and an outcome (no reverse causality).

Disadvantage

 Long period of follow-up.

 Not good for rare diseases.

 Attrition: loss of participants due to death, migration, disinterest.

Case-control studies

A study that compares patients who have an outcome of interest (cases) with patients who do not have the outcome (controls), and looks back to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk factor and the outcome.

Types

 Non-matched case-control

-The simplest form (and old).

-Select subjects with the disease.

-Select controls without the disease.

 Matched case-control

Select subjects with the disease and match them with control with similar characteristics (e.g. sex, age, weight).

 Nested case-control studies

A case-control study in which cases and controls are drawn from the population in a fully enumerated cohort.

Advantages

 Inexpensive (compared to cohort studies).

 Good for rare diseases.

 Useful for studying multiple exposures to the same diseases.

Disadvantages

 Selection, recall, information bias.

 Not good for rare exposures.

 Not useful in multiple outcomes.

Ecological studies

An observational study is defined as examining the association between an exposure and an outcome, namely at the population or group level, rather than the individual level.

They are inexpensive and easy to carry out, using routinely collected data, but they are prone to bias and confounding.

Advantages

 The purpose of the study is to monitor population health so that public health strategies may be developed.

 The purpose of the study is to make large-scale comparisons, e.g. comparisons between countries.

Disadvantages

 Inaccuracy of data.

 Inability to control confounders.

Case report

A detailed report of symptoms, signs, diagnosis and treatment of an individual patient.

Usually describe an unusual or novel occurrence:

 Unusual side effects to therapy.

 Previously unreported disease.

 Unique use of diagnostic tests.

 Unique or rare feature of a disease.

 Unusual presentation.

 New diagnosis method.

Advantages

 Can be shared for medical and educational purposes.

 Useful in rare conditions

 Generate potential hypotheses for future studies.

Disadvantages

 Data cannot be quantified, also, there is no comparison so cannot be generalized, except in specific patients.

Case series

A study that describes a set of patients who show similar symptoms or outcomes. Almost as case reports, but differ in number. There is no control group.

Types

 Case series

 Retrospective case series: uses existing data such as medical records.

 Consecutive case series: includes all eligible patients identified by the researchers during the study registration period. The patients are treated in the order in which they are identified.

Advantages

 Can be shared for medical and educational purposes.

 Useful in rare conditions.

 Generate potential hypotheses for future studies.

Disadvantages

 Data cannot be quantified and there is no comparison so cannot be generalized except in specific patients.

Longitudinal studies Definition

A type of correlational research in which researchers observe and collect data on a number of variables without trying to influence those variables.

The opposite of a longitudinal study is a cross-sectional study. While longitudinal studies repeatedly observe the same participants over a period of time, cross- sectional studies examine different samples (or a “cross-section”) of the population at one point in time.

Types of longitudinal studies

They are generally observational, however, may also be experimental. Some of these are briefly discussed below:

1. Repeated cross-sectional studies where study participants are largely or entirely different on each sampling occasion.

2. Prospective studies

Cohort panels: wherein some or all individuals in a defined population with similar exposures or outcomes are considered over time.

Representative panels: where data is collected for a random sample of the population..

Linked panels: wherein data collected for other purposes is tapped and linked to form individualspecific datasets.

3. Retrospective studies

Designed after at least some participants have already experienced events that are of relevance; with data for potential exposures in the identified cohort being collected and examined retrospectively.

Advantages of longitudinal studies

 The ability to identify and relate events to particular exposures, and to further define these exposures with regards to presence, timing and chronicity.

 Allow researchers to follow their subjects in real time. This means you can better establish the real sequence of events, allowing you insight into cause-and-effect relationships.

 Allow repeated observations of the same individual over time. This means any changes in the outcome variable cannot be attributed to differences between individuals.

 Prospective longitudinal studies (as cohort studies ) eliminate the risk of recall bias, or the inability to correctly recall past events.

 Ability to correct for the “cohort effect” that is, allowing for analysis of the individual time components of cohort (range of birth dates), period (current time), and age (at point of measurement) and to account for the impact of each individually.

Disadvantages

 Time-consuming and often more expensive than other types of studies, so they require significant commitment and resources to be effective.

 Since longitudinal studies repeatedly observe subjects over a period of time, any potential insights from the study can take a while to be discovered

 Attrition, which occurs when participants drop out of a study, is common in longitudinal studies and may result in invalid conclusions.

 The potential for inaccuracy in conclusion if adopting statistical techniques that fail to account for the intra-individual correlation of measures.

Interventional studies (clinical trials)

Definition

Scientific experiment that is done prospectively in clinical research in which researchers introduce an intervention and study the effect of it either as a:

1. Diagnostic: such as new methods or tests for diagnosis of a disease or condition.

2. Preventive: such as vaccines.

3. Therapeutic: as any new treatment for a specific condition or detection of the effect of present treatment on another condition.

Importance and Advantages

 Provide a causative relationship between exposure to a certain risk factor and outcome.

 Test and evaluate the safety and the efficacy of the intervention.

 Control over risk assignment.

 Provide strong evidence ( Randomized control trials are gold standard studies by their high internal validity ).

Disadvantages

 Expensive.

 Time consuming.

 Sometimes expose participants to potential harm.

 May be difficult, inappropriate or unethical.

Differences between it and observational study

Observational studies

Researchers merely document the presence of exposure(s) and outcome(s) as they occur, without trying to alter the course of natural events.

Interventional studies

The researcher actively interferes with nature – by performing an intervention in some or all study participants – to determine the effect of exposure to the intervention on the natural course of events