scientists do their experimental tests more than once, so they can reduce the effects of chance errors is called conducting __________?

I believe it is "trials".

Scientists conducting experimental tests more than once to reduce the effects of chance errors is called conducting "replicates" or "replications." Replication is an essential practice in scientific research to ensure the reliability and validity of experimental findings. By conducting multiple replicates of an experiment, scientists can account for variability and minimize the influence of random fluctuations, increasing confidence in the results.