Validity is an important dimension of psychological research. Due to the diversity and complexity of psychological research objects, there are many factors that may endanger validity. Psychological researchers use various control strategies to improve validity. In recent years, repetition, especially emphasized in the field of psychology, is actually a control strategy.

1、 The meaning of repetition

When researchers do an experiment, they often get the expected results. However, this positive result may be just a coincidence, that is, it may be false - the fact that researchers usually confirm the tendency increases the possibility. In order to avoid this situation, especially to prevent research fraud, the scientific field needs to repeat those important studies. In fact, unrepeatable one-off events emerge one after another in scientific research (coolican, 2014) - such events are exciting at first, then questioned, and then forgotten.

Repetitive research is particularly important in psychology because it studies extremely diverse and flexible human behaviors. The number of human beings is huge, and human behavior is extremely diverse. Psychological research can only extract samples from the human population, and can only select samples of human behavior to estimate human behavior. That is to say, psychological research can not test everyone, but can only study the sample of subjects and behavior samples, and then extend the corresponding research findings to the corresponding behavior and the whole human. In order to show that a psychological effect is true, psychology needs different researchers to repeat the findings. When the findings are controversial or contradictory to the existing findings, repetition is particularly important.

2、 Types of repetition

There are two types of repetition in scientific research: direct repetition and systematic repetition (McBurney, 1990). Direct repetition is a kind of research that researchers try to do completely according to the original research in order to get the same findings. Systematic repetition is a kind of research based on the original research and through certain changes.

In psychological research, systematic repetition is usually carried out, that is, researchers carry out their own research based on the existing research, through in-depth thinking and logical reasoning, with different subjects, different materials, different variable values and different operation definitions, which is an extension or improvement of the original research. At this point, if the original study is correct, the researcher will get the specific results consistent with the original study.

In psychological research, direct repetition usually occurs when systematic repetition fails. Researchers return to the original research and repeat it with the same method of the original research, trying to find the differences between their own research and the original research. In the context of repeatability crisis, a few years ago, the field of psychology carried out a systematic direct repetition.

In order to replicate, researchers need to obtain details of the original study. Psychological research ethics requires researchers to share data, procedures and measurements. If a psychological researcher cannot clearly describe the prediction, method and result of his / her work, then he / she claims that the effect found is false. The prediction, method and result of a psychological research should be available for others to test.

3、 Repetition is control

As mentioned above, repetition (especially systematic repetition) is the norm in psychological research. As long as the results of the repeated study are consistent with those of the original study, the original study is supported, which is to test the internal validity. In order to test the external validity, the system repeatedly uses different subjects, different stimuli, different situations and at different times. Systematic repetition with different operational definitions of theoretical concepts is to test the construct validity. For statistical validity, both direct and systematic repetitions were tested. Therefore, from the perspective of control as a test of validity, repetition is a control strategy (McBurney, 1990).

4、 The difficulty of repetition

At the beginning of the question, the students are often pointed out that "you are repeating other people's research" and "you are repeating other people's work". This is a paradox: on the one hand, we all know the importance of repetition in science; on the other hand, we tend to disapprove of repetitive research. Of course, the problem is that researchers who actually repeat others' research often do not demonstrate the value and significance of their own research from the perspective of repeating others' research. On the contrary, they always want to demonstrate the innovation of their own research, that is, they regard repetitive research as innovative research. In fact, it also reflects that some psychological researchers have not fully and correctly understood the significance of repetitive research.

At the same time, journals (especially prestigious journals) are reluctant to publish repetitive research papers. Although we all know that repetition is the cornerstone of science, many journals are not interested in direct repetition, especially in negative repetitive research - journals only want to publish research papers that report novel positive findings.

If we strengthen the understanding of repetitive research from the perspective of control, especially with reference to the validity of psychological research, then the field of psychology will gradually have a reasonable understanding of repetitive research, which is also beneficial to the proper interpretation of the repeatability crisis.