Without the use of a comparison or control group, has little control over the factors that affect the validity of the results.
in an experiment, the group exposed to the treatment, that is, to one version of the independent variable
Type of study
non-intervention - observationalinnervation - measure the out come
Types of descriptive studies
1. Case report:- a careful, detailed report by one or more clinicians of the profile of a single patient2. Ecological studies - data from entire populations are used to compare disease frequencies between different groups during the same period of time or in the same population at different points in time3. Cross-sectional studies -provides information concerning the situation at a given time
follow descriptive studies, and are used to identify the cause of the health problemObservational intervention
a study based on data in which no manipulation of factors has been employedeg comparative cross-sectional • cohort • case-control study
Comparative cross-sectional studies
Depending on the purpose of a given study, a cross-sectional survey could have an analytical component
the study of a group of people who share a common characteristic and move forward in time as a unit1. Strengths of the cohort study - Is of particular value when the exposure is rare • Can examine multiple effects of a single exposure 2. limitations of the cohort study - Is inefficient for the evaluation of rare diseases • Expensive and time-consuming
assess outcome status and then assess for exposure history1. Strengths of the cohort study - relatively quick and inexpensive • optimal for the evaluation of rare diseases.2. limitations of the cohort study - • inefficient for the evaluation of rare exposures • Cannot directly compute incidence rates of disease in exposed and non-exposed individuals.
• researcher manipulates a situation and measures the effects of this manipulation.1• experimental studies 2• quasi-experimental studies
1• experimental studies
gives the most reliable proof for causation. 1• individuals are randomly allocated to at least two groups2. One group is subject to an intervention, or experiment, while the other group(s) is not. 2• widely used in laboratory settings and in clinical settings
2• quasi-experimental studies
1. one characteristic of a true experiment is missing, either randomization or the use of a separate control group.2• always includes the manipulation of an independent variable which is the intervention. 3• uses two (or more) groups, one of which serves as a control group in which no intervention takes place.