To repeat an experiment, under the same conditions, allows you to (a) estimate the variability of the results (how close to each other they are) and (b) to increase the accuracy of the estimate (assuming that no bias – systematic error – is present).

Why does repeating increase reliability?

You can test reliability through repetition. The more similar repeated measurements are, the more reliable the results. ... However, the entire result of the experiment can be improved through repetition and analysis, as this may reduce the effect of random errors.

Does repeating an experiment increase accuracy or precision?

The accuracy of a measurement is dependent on the quality of the measuring apparatus and the skill of the scientist involved. For data to be considered reliable, any variation in values must be small. Repeating a scientific investigation makes it more reliable.