They are characterized because the researcher cannot intentionally manipulate the VI or randomly assign subjects to different levels of it. The subjects are not random. Subjects are selected based on whether or not they possess certain characteristics. Subjects are selected after VI has occurred. The relationships of “pre-existing” variables are studied.
The VI can be: Organismic: sex, age, personality characteristic, intelligence, anxiety, illness…etc. Outside the body: having experienced a catastrophe, belonging to an educational system, social environment…etc.
There are two research strategies, which will be divided into designs following Leon Montero: Retrospective: The causal process has already occurred and it is about searching (reconstructing the facts) for the possible causes that caused them. Prospective: VI is known (not DV) but its consequences have not been evaluated.
General characteristics
I saw her: the values are given. There is no intentional manipulation of this variable, but rather “selection of values.” Causal relationships cannot be established as in the experiment. You can only study the relationship between variables that covary with the phenomenon studied. To establish causal relationships, 3 requirements must be met:
- Existence of covariation between the VI and the VD.
- The VI must precede the VD.
- Relevant explanations must be ruled out.
These designs only fulfill the first and sometimes the second, but not the third. Therefore, although we talk about VI and VD, the difference between both variables is merely theoretical. When the ex post facto design is a comparison of groups, hypotheses are formulated in which a differential relationship is established between the groups.
Kerlinger (1984) In ex post facto research, inferences are made about the relationship between the variables, without direct intervention, based on the concomitant variation of the VVII and the VVDD. Although this design has less internal validity than the experimental one, it gains external validity, since research is usually carried out in natural situations and with no more representative than experiments, also in terms of subjects and variables. It is very useful in the applied field, since it allows us to address issues that could not be investigated using the experimental method.
Control techniques
To establish the existing relationship between the variables, we must control the possible VVEE: Alvarado (2000) points out three procedures:
- The pairing or pairing of subjects: The use of subject variables and the impossibility of randomization. It consists of selecting for each group, subjects with equal values in the most relevant VVEE (E.G.: if we are studying the relationship between depression-VI- and work absenteeism-VD- we can match the subjects in other variables related to work absenteeism , such as: level of education, level of anxiety, illnesses suffered, etc. Groups of subjects would be formed that had equal levels of these variables).
- Analysis of covariance (ANCOVA): control technique on VVEE, which requires the use of representative samples. Control through statistical procedures carried out after data collection. It eliminates the influence of the disturbing variable on the VD, purifying the effect of the VI on the VD.
- Introduction of variables related to DV. Uses several VVDD instead of just one (E.G. Absenteeism VI, VVDD depression and job satisfaction) > Next: Part 1: Classification of Ex post facto designs
Use of ex post facto designs in applied research
Clinical psychology: to establish diagnostic categories or make predictions about diagnosis and therapy 50s to evaluate the effects of psychotherapy. Neurophysiological investigations: The functions of the hemispheres have been studied using simple prospective designs (in this type of research, subjects are selected according to the brain lesions they suffer and their behavior is observed).
Epidemiological investigations: study of health and illness in human populations (includes diseases, quality of health, and mental health).
- Descriptive studies: The survey methodology is used and is carried out when little is known about the occurrence, natural or specific history of a disease. Estimate the frequency or trend of a disease in a particular population and generate specific etiological hypotheses.
- Etiological studies: when the disease is well known and there are specific hypotheses. Identify risk factors for the disease, estimate their effects on the disease, and suggest possible intervention strategies.
- Educational field: in the study of variables related to academic performance or success (self-concept, sex, aptitude, cultural or racial differences, etc.). Developmental psychology: research that seeks to establish the relationship between age and the use of learning strategies, memorization, etc.
This article is merely informative, at Psychology-Online we do not have the power to make a diagnosis or recommend a treatment. We invite you to go to a psychologist to treat your particular case.
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