What Is Replication?

Why many psychology studies fail to replicate

Researchers working on a replication study
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Replication is a term referring to the repetition of a research study, generally with different situations and different subjects, to determine if the basic findings of the original study can be applied to other participants and circumstances.

Once a study has been conducted, researchers might be interested in determining if the results hold true in other settings or for other populations. In others cases, scientists may want to replicate the experiment to further demonstrate the results.

For example, imagine that health psychologists perform an experiment showing that hypnosis can be effective in helping middle-aged smokers kick their nicotine habit. Other researchers might want to replicate the same study with younger smokers to see if they reach the same result.

Why Is Replication So Important In Psychology?

When studies are replicated and achieve the same or similar results as the original study, it gives greater validity to the findings. If a researcher can replicate a study’s results, it means that it is more likely that those results can be generalized to the larger population.

How Do Scientists Replicate an Experiment?

When conducting a study or experiment, it is essential to have clearly defined operational definitions. In other words, what is the study attempting to measure?

When replicating earlier researchers, experimenters will follow the same procedures but with a different group of participants.

If the researcher obtains the same or similar results in follow-up experiments, it means that the original results are less likely to be a fluke.

What if Replication Fails?

So what happens if the original results cannot be reproduced? Does that mean that the experimenters conducted bad research or that, even worse, they lied or fabricated their data?

In most cases, non-replicated research is caused by differences in the participants or in other extraneous variables that might influence the results of an experiment. Sometimes the differences might not be immediately clear and in others researchers might be able to discern which variables might have impacted the results.

For example, minor differences in things like the way questions are presented, the weather or even the time of day the study is conducted might have an unexpected impact on the results of an experiment. Researchers might strive to perfectly reproduce the original study, but variations are expected and often impossible to avoid.

Are the Results of Psychology Experiments Hard to Replicate?

In 2015, a group of more than 250 researchers published the results of their five-year effort to replicate 100 different experimental studies previously published in three top psychology journals. The replicators worked closely with the original researchers of each study in order to replicate the experiments as closely as possible.

The results were less than stellar. Of the 100 experiments in question, 64 percent could not replicate the original results. Of the original studies, 97 percent of the findings were deemed statistically significant.

Only 36 percent of the replicated studies were able to obtain statistically significant results.

As one might expect, these dismal findings caused quite a stir.

So why are psychology results so difficult to replicate? Writing for The Guardian, John Ioannidis suggested that there are a number of reasons why this might happen, including competition for research funds and the powerful pressure to obtain significant results. There is little incentive to retest, so many results obtained purely by chance are simply accepted without further research or scrutiny.

The project authors suggest that there are three key reasons why the original findings could not be replicated.

  • The original results were a false positive.

  • The replicated results were a false negative.

  • Both studies were correct but differed due to unknown differences in experimental conditions or methodologies.

How Replication Can Be Strengthened

The Nobel-prize winning psychologist Daniel Kahneman has suggested that because published studies are often too vague in describing methods used, replications should involve the authors of the original studies in order to more carefully mirror the methods and procedures used in the original research. In fact, one investigation has found that when original researchers are involved, replication rates are much higher.

While some might be tempted to look at the results of such replication projects and assume that psychology is rubbish, many suggest that such findings actually help make psychology a stronger science. Human thought and behavior is a remarkably subtle and ever-changing subject to study, so variations are to be expected when observing diverse populations and participants.

Some research findings might be wrong, but digging deeper, pointing out the flaws, and designing better experiments helps strengthen the field.



    Ionnidis, J. Psychology experiments are failing the replication test - for good reason. The Guardian; 2015.

    Makel, M. C.; Plucker, J. A.; Hegarty, B. Replications in Psychology Research How Often Do They Really Occur?. Perspectives on Psychological Science. 2012; 7(6): 537–542.

    Open Science Collaboration. Estimating the reproducibility of psychological science. Science. 2015; 349 (6251), aac4716. Doi: 10.1126/science.aac4716.

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