What type of validity is most concerned with whether there is a relationship between the variables?

A confounding variable is an extraneous variable that is statistically related to (or correlated with) the independent variable. This means that as the independent variable changes, the confounding variable changes along with it. Failing to take a confounding variable into account can lead to a false conclusion that the dependent variables are in a causal relationship with the independent variable. Take, for example, a hypothetical study that found that people who carry a lighter in their pocket tend to have higher rates of cancer. It would be incorrect to conclude that there is a direct relationship between these two variables or that carrying a lighter in one’s pocket causes cancer. Instead, there is a confounding variable of smoking; people who carry a lighter in their pocket are more likely to be smokers, and those who smoke are more likely to be diagnosed with cancer. Researchers should be careful to identify and control for potential confounding variables so that associations between the dependent variable and the independent variable can be accurately identified and measured.

The remainder of this short course in research methods will examine various threats to validity that exist at each stage of the research process. Validity refers to whether a study is well-designed and provides results that are appropriate to generalize to the population of interest. Trochim’s “Research Methods Knowledge Base” provides a succinct and useful summary of each type of validity; the three main types of validity with which a researcher should be concerned are discussed in this module.(1)

Internal Validity

Internal validity applies in studies that seek to establish a causal relationship between two variables and refers to the degree to which a study can make good inferences about this causal relationship. Internal validity is achieved when a researcher can definitively state that the effects observed in the study were due to the manipulation of the independent variable and not due to another factor. Variables outside the researcher’s control or consideration can affect the outcome of a study and can therefore prevent internal validity.(2)

Construct Validity

Construct validity is closely related to the process of operationalizing which we discussed in Module 1.  It refers to the extent to which a researcher can claim that accurate inferences can be made from the operationalized measures in a study for the theoretical constructs on which they were based.  Construct validity is concerned with generalizing from the specificities of a study to the broader concept that the study attempts to measure or draws conclusions.  A study is considered to have construct validity if the researcher can demonstrate that the variables of interest were properly operationalized.(3) For example, if, in the Module 1 example of near-sighted individuals obtaining corrective lenses, the researcher had chosen to operationalize “economically productive” as “the amount of money a person has in his or her savings,” the researcher would have obtained entirely different results. It is possible for people to have other sources of income (gifts, spouse’s income, inheritances, etc.) other than personal weekly wages that may affect this variable, meaning that amount of money in savings is not a good measure of economic productivity; this therefore affects the construct validity of the study.

External Validity

A researcher often cannot work with the entire population of interest but instead must study a smaller sample of that population in order to draw conclusions about the larger group from which the sample is taken. External validity involves the extent to which the conclusions can be generalized to the broader population. A study is considered to be externally valid if the researcher’s conclusions can in fact be accurately generalized to the population at large.(4) The sample group must be representative of the target population to ensure external validity.

As a researcher, it is important to keep the concept of validity in mind at all times when designing a study. A good researcher will discuss the project design with an advisor or a group of colleagues to help ensure that validity is preserved at every stage of the process. A research project that lacks validity may draw conclusions that are inappropriate or even dangerous if applied to the target population.

For more information about how to ensure the validity of research, please review Research Validity.

Footnotes

(1) Trochim, W. M. K.  “Design” Research Methods Knowledge Base 2nd Edition.

(4) Pelham, B. W.; Blanton, H. Conducting Research in Psychology: Measuring the Weight of Smoke, 3rd Edition.  Wadsworth Publishing (February 27, 2006).

Validity refers to the state in which the researcher or the investigator can get assurance that the inferences drawn from the data are error free or accurate. If there is validity in the sample, then it is in the population from where that sample has been drawn.

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There are basically four major types of Validity. These types are Internal, External, Statistically Conclusive and Construct.

Internal Validity refers to the type where there is a causal relationship between the variables. It signifies the causal relationship between the dependent and the independent type of variable. Internal Validity refers to those factors that are the reason for affecting the dependent variable. This type is used in the case of the design of experiments where the treatments are randomly assigned.

External Validity refers to the type where there is a causal relationship between the cause and the effect. The cause and effect are those that are generalized or transferred either to different people or different treatment variables and the measurement variable.

Statistically Conclusive Validity refers to the type in which the researcher is interested about the inference on the degree of association between the two variables. For instance, in the study of the association between the two variables, the researcher reaches statistically conclusive validity only if he has performed statistical significance tests upon the hypotheses predicted by him. This type is violated when the researcher reaches two types of errors, namely type I error and type II error.

Type I error causes violation of this type of validity because in this type of error, the researcher rejects the hypothesis which was indeed true.

Type II error causes violation of this type of validity because in this type of error, the researcher accepts the hypothesis which was indeed false.

Construct Validity refers to the type in which the construct of the test is involved in predicting the relationship for the dependent type of variable. For example, construct validity can be drawn with the help of Cronbach’s alpha. In Cronbach’s alpha, it is assumed that if its value is 0.80, then it is considered good for confirmation, and if its value is 0.70, then it is adequate. So, if the construct satisfies such conditions, then the validity holds. Otherwise, it does not.

Convergent/divergent validation and factor analysis is also used to test this type of validity.

There is a strong relationship between validity and reliability. A test is said to be unreliable if it does not hold the conditions of validity. Reliability is a necessary property of the test, but is not the sufficient condition.

Thus, validity plays the significant role in making an accurate inference about the data.

There are certain things that act as a threat to validity. These are as follows:

If the researcher collects insufficient data to attain this in the inference, this is not feasible because insufficient data will not represent the population as a whole.

If the researcher measures the sample of the population with too few measurement variables, then he also cannot achieve validity of that sample.

If the researcher selects the wrong type of sample, then he too cannot achieve validity in the inference about the population.

If the researcher selects an inaccurate measurement method during analysis, then the researcher would not be able to achieve validity.

What type of validity is most concerned with whether the results can be generalized to other persons places and times?

What is internal vs external validity?

What is meant by internal validity?

Is internal or external validity more important?