In their introduction to the special issue of The American Statistician on the topic, the journal’s editors urge “moving to a world beyond ‘p<0.05,’” the famous 5 percent threshold for determining whether a study’s result is statistically significant. If a study passes this test, it means that the probability of a result being due to chance alone is less than 5 percent. This has often been understood to mean that the study is worth paying attention to.
The journal’s basic message – but not necessarily the consensus of the 43 articles in this issue, one of which I contributed – was that scientists first and foremost should “embrace uncertainty” and “be thoughtful, open and modest.”
While these are fine qualities, I believe that scientists must not let them obscure the precision and rigor that science demands. Uncertainty is inherent in data. If scientists further weaken the already very weak threshold of 0.05, then that would inevitably make scientific findings more difficult to interpret and less likely to be trusted.
Piling difficulty on top of difficulty
In the traditional practice of science, a scientist generates a hypothesis and designs experiments to collect data in support of hypotheses. He or she then collects data and performs statistical analyses to determine if the data did in fact support the hypothesis.
One standard statistical analysis is the p-value. This generates a number between 0 and 1 that indicates strong, marginal or weak support of a hypothesis.
Repapetilto/Wikimedia, CC BY-SA
But I worry that abandoning evidence-driven standards for these judgments will make it even more difficult to design experiments, much less assess their outcomes. For instance, how could one even determine an appropriate sample size without a targeted level of precision? And how are research results to be interpreted?
These are important questions, not just for researchers at funding or regulatory agencies, but for anyone whose daily life is influenced by statistical judgments. That includes anyone who takes medicine or undergoes surgery, drives or rides in vehicles, is invested in the stock market, has life insurance or depends on accurate weather forecasts… and the list goes on. Similarly, many regulatory agencies rely on statistics to make decisions every day.
Scientists must have the language to indicate that a study, or group of studies, provided significant evidence in favor of a relationship or an effect. Statistical significance is the term that serves this purpose.
The groups behind this movement
Hostility to the term “statistical significance” arises from two groups.
The first is largely made up of scientists disappointed when their studies produce p=0.06. In other words, those whose studies just don’t make the cut. These are largely scientists who find the 0.05 standard too high a hurdle for getting published in the scholarly journals that are a major source of academic knowledge – as well as tenure and promotion.
The second group is concerned over the failure to replicate scientific studies, and they blame significance testing in part for this failure.