INTERNAL VALIDITY: HOW IT IS ACHIEVED, THREATS, EXAMPLES - CULTURE VOCABULARY - 2025

The internal validity is a fundamental concept for research methodology as it determines the degree of reliability of the experiments and interpretations drawn from them.

An experimental research process needs strict control of all influencing factors for it to have internal validity. When we speak of control, we refer to the accurate knowledge of the relationship between the independent and dependent variables and how they affect each other to determine the results.

Internal validity guarantees reliability in investigations. Source: pixabay.com

That is, the control allows us to identify the causality of the changes that occurred in the variables of an experiment.

To achieve this, it should be avoided that other variables that do not apply within the hypothesis under test intervene in the change of the dependent variables; only then will it be known whether the independent variables influence them.

To achieve internal validity, it is necessary to isolate the specific relationships that are studied between the independent and dependent variables, to prevent the experiment from being “contaminated”.

How to achieve internal validity

To achieve control - and consequently, the internal validity of an experiment - the first thing to bear in mind is that you must have a minimum of two experimental comparison groups.

If we were to experiment with a single group, it would be impossible to know if there was no other influence factor other than the independent variable that was manipulated. For example, to know if a fertilizer has an effect on the growth of a plant, you have to compare the treated plant with another that has not been.

Furthermore, these comparison groups must be exactly the same in everything except the way the independent variables being tested are manipulated.

If it is known that the control groups are the same in everything except in the way in which they were exposed to the independent variables, the changes they undergo in the experiment should be attributed to these variables; that is, it would be known that the dependent variables were caused by the independent ones.

Threats to internal validity

The possible sources of internal invalidation are external explanations to the variables contemplated within the experiment and that threaten the reliability of the conclusions reached by the research.

External factor interruption

The first great threat is that some of the participants or objects of study suffer some event outside the experience of the others during the tests. This would eliminate the equivalence of the experimental and control groups.

Therefore, the scientist must ensure that each of the objects of study experience exactly the same events.

Instrumentation

Another threat to internal validity is the instability of the instrument for measuring results.

To avoid this affecting the experiment, it is necessary to previously check the stability of the instrument, repeating several tests measured with said instrument over an extended period and verifying repeatability patterns without anomalies in the results.

It is also necessary to take into account that the measuring instrument must be the same for each experimental group.

The experimental environment

Apart from the measuring instrument, the experimental environment must also be taken into account. This must be controlled and it must be ensured that all study objects, experimental and control, are under the same conditions.

Human factors

It is necessary to verify that at the time of beginning the experiment all the participants or study objects present normal data regarding the measured variables, that they are not going through a process that alters the real assessment of the characters studied.

Another possible threat is that study subjects interrupt research by abandoning it in the middle of the process. To solve this problem, it is necessary to replace the subject with one that is similar.

The human factor in experimental research processes is one of the most unstable. The researcher should try to keep the study subjects motivated by means of compensation so that as far as possible the subjects are the same from the beginning to the end of the investigation.

If the subjects studied are human beings, care must be taken that they do not communicate with each other, since the information that they can share about the different variables they experience can affect the natural development of the research.

Another human factor to take into account (apart from the attitude of the study subjects) is the attitude of the researcher himself. This at all times must seek objectivity, behave in the same way and perform the same procedures with all subjects and objects of study.

Examples of internal validity

Example 1

Suppose you want to investigate the effect of a television commercial on the consumer's predisposition to purchase the advertised product.

To make a valid experiment in this case there should be at least two groups: one that has seen the commercial and one that has not seen it.

Furthermore, external variables should be controlled. It could be the case that some of the study subjects have heard about the product from their friends or that they have previously tried it and, therefore, have first-hand knowledge of its characteristics and qualities.

These are aspects that would affect the consumer's perception of the product and have nothing to do with the independent variable studied: exposure to the commercial. For this reason, the ideal would be to choose study subjects who have not been exposed to these variables.

Example 2

Another example may be an investigation into the influence of a pedagogical method on the learning process.

For a study of this type, the equivalence of the study subjects is extremely important, both in the experimental and control groups, since variables such as the disparity in the intellectual capacity of the participants could be present.

Before conducting the experiment, the possibility of excessive disparity in the willingness of the subjects to learn must be ruled out; otherwise, the study would lack internal validity.

Reference

1. "Stability" (sf) in Infas Control. Retrieved on July 11, 2019 from Infas Control: infas.com.ar
2. Internal validity (nd) in Indiana. Retrieved on July 11, 2019 from Indiana: indiana.edu
3. Baptista, P., Fernández, C. & Hernández Sampieri, R. “Research Methodology” (2014). Mexico DF: McGraw-Hill / Interamericana
4. Cepeda, M. and Quezada, M. "Research Design, Internal Validity and External Validity" (March 26, 2016) in SlideShare. Retrieved on July 11, 2019 from SlideShare: es.slideshare.net
5. Cuncic, A. "Understanding Internal and External Validity" (June 20, 2019) in VeryWell. Retrieved on July 11, 2019 from VeryWellMind: verywellmind.com