OUTLIER Definition & Usage Examples

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What is an outlier

This can potentially help you disover inconsistencies and detect any errors in your statistical processes. An outlier can distort the correlation to make it seem that there is a strong relationship when, in fact, there is nothing but randomness and one outlier. An outlier can also distort the correlation to make it seem that there is no relationship when, in fact, there is a strong relationship and one outlier. A data point in a scatterplot is a bivariate outlier if it does not fit the relationship of the rest of the data. An outlier can distort statistical summaries and make them very misleading.

An outlier is a single data point that goes far outside the average value of a group of statistics. Outliers may be exceptions that stand outside individual samples of populations as well. In a more general context, an outlier is an individual that is markedly different from the norm in some respect. In this article you learned how to find the interquartile range in a dataset and in that way calculate any outliers.

Origin of outlier

You’ll get a unique number, which will be the number in the middle of the 5 values. Since there are 11 values in total, an easy way to do this is to split the set in two equal parts with each side containing 5 values. In the Configuration Dialog, for Output location, click on Browse and navigate to Tutorial_2 folder. In the Configuration Dialog, note that all variables are selected automatically as to be included.

What is an outlier

Outliers arise due to changes in system behaviour, fraudulent behaviour, human error, instrument error or simply through natural deviations in populations. A sample may have been contaminated with elements from outside the population being examined. Alternatively, an outlier could be the result of a flaw in the assumed theory, calling for further investigation by the researcher.

Alternative models

In data mining literature, normal data are also known as “inliners” (Aggarwal, 2017). Often in real-world applications, such as fraud or intrusion detection system, outliers are sequential and not single datapoints within a sequence. For instance, network intrusion is an event in a sequence that is intentionally caused by an individual. Properly identifying the anomalous event helps to handle those sequences. Outliers may occur because of correct data capture (few people with income in tens of millions) or erroneous data capture (human height as 1.73 cm instead of 1.73 m). Regardless, the presence of outliers needs to be understood and will require special treatments.

  1. They can also indicate an anomaly or something of interest to study since it’s not always possible to determine if outliers are in error.
  2. More specifically, the data point needs to fall more than 1.5 times the Interquartile range above the third quartile to be considered a high outlier.
  3. Real datapoints that are generated from noisy environments are difficult to detect using scores.

This means that a data point needs to fall more than 1.5 times the Interquartile range below the first quartile to be considered a low outlier. This represents that the automatic removal of outliers might be too strict; therefore, a manual process to remove outliers might be better. Since the next highest value is 84, a value of 240 seems an input error, and the outlier 14 records should be removed. Right-click on the Statistics node and select Occurrences Table. To find any lower outliers, you calcualte Q1 – 1.5(IQR) and see if there are any values less than the result. This is the difference/distance between the lower quartile (Q1) and the upper quartile (Q3) you calculated above.

How to calculate IQR in an odd dataset

The purpose of creating a representative model is to generalize a pattern or a relationship within a dataset and the presence of outliers skews the representativeness of the inferred model. Detecting outliers may be the primary purpose of some data science applications, like fraud or intrusion detection. Outliers can occur by chance in any distribution, but they can indicate novel behaviour or structures in the data-set, measurement error, or that the population has a heavy-tailed distribution. A frequent cause of outliers is a mixture of two distributions, which may be two distinct sub-populations, or may indicate ‘correct trial’ versus ‘measurement error’; this is modeled by a mixture model. The possibility should be considered that the underlying distribution of the data is not approximately normal, having “fat tails”.

What is an Outlier? Definition and How to Find Outliers in Statistics

Next, to find the lower quartile, Q1, we need to find the median of the first half of the dataset, which is on the left hand side. The rule for a low outlier is that a data point in a dataset has to be less than Q1 – 1.5xIQR. This article will explain how to detect numeric outliers by calculating the interquartile range. When deciding whether to remove an outlier, the cause has to be considered. Connect the output triangle of the Table Writer node to the left triangle of the Math Formula node. Connect the output triangle of the Column Filter node to the left triangle of the Math Formula node.

How to calculate Q1 in an odd dataset

You should always watch out for outliers in bivariate data by looking at a scatterplot. If you can justify removing an outlier (eg, by finding that it should not have been there in the first place), then do so. If you have to leave it in, at least be aware of the problems it can cause and consider reporting statistical summaries (such as the correlation coefficient) both with and without the outlier. There are no lower outliers, since there isn’t a number less than -8.5 in the dataset.

Outliers are an important factor in statistics as they can have a considerable effect on overall results. In especially small sample sizes, a single outlier may dramatically affect averages and skew the study’s final results. An outlier can happen due to disinformation by a subject, errors in a subject’s responses or in data entry. In some cases, it’s clear that outliers should be removed as errors.

Outliers exhibit a certain set of characteristics that can be exploited to find them. Following are classes of techniques that were developed to identify outliers by using their unique characteristics (Tan, Steinbach, & Kumar, 2005). Each of these techniques has multiple parameters and, hence, a data point labeled as an outlier in one algorithm may not be an outlier to another.

The choice of how to deal with an outlier should depend on the cause. Some estimators are highly sensitive to outliers, notably estimation of covariance matrices.