Replication of Experiments
Considerable confidence is added if an experiment is replicated by other researchers. This helps confirm that the previous results weren't dependent on some unreported aspect of the first experiment and that it wasn't the result of a statistical fluke or sloppy or fraudulent work.
Researchers don't make their reputations by duplicating other people's work, however, so often only the most important experiments are replicated directly. One of these was in the well-known "cold fusion" announcement, where the claim was so extraordinary and economically important that quite a few research teams attempted replications, ultimately without success. It may be more common that researchers will undertake similar experiments with moderate changes, like testing another vegetable related to radishes or testing radishes on people in a different age group. While we wouldn't expect all tests of slightly different situations to succeed, if none of them did, we would begin to expect that the original results might have been wrong. If a lot of near-replications do succeed, we would be justified in thinking the original experimental result was confirmed.