 Error is any deviation of study results from truth. When this error happens randomly in all directions, it is called as random error. It is inevitably present in any kind of study and it can be reduced only by increasing the sample size. When this error causes systematic deviations from truth in a particular direction, then it is called as systematic error or bias. It cannot be minimized by increasing the sample size. It can be minimized only by increasing the quality of the study. A study with more random error is not precise, but a study with systematic error or bias is not accurate.