what is an outlier in statistics

An outlier in statistics is an observation that lies an abnormal distance from other values in a random sample from a population. In other words, it is a data point that differs significantly from other observations. Outliers can be extremely high or extremely low values that are far from other data points. Outliers can be problematic for many statistical analyses because they can cause tests to either miss significant findings or distort real results. However, outliers can also contain important information about the process under investigation or the data gathering and recording process, so they should be investigated carefully before considering their elimination from the data. There are no strict statistical rules for definitively identifying outliers, but there are guidelines and statistical tests that can be used to find outlier candidates. Some outliers represent natural variations in the population and should be left as is in the dataset, while others are problematic and should be removed because they represent measurement errors, data entry or processing errors, or poor sampling.