An outlier is **an observation that lies an abnormal distance from other values in a random sample from a population**. In a sense, this definition leaves it up to the analyst (or a consensus process) to decide what will be considered abnormal. … These points are often referred to as outliers.

## How do you identify outliers?

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If we **subtract 1.5 x IQR from the first quartile**, any data values that are less than this number are considered outliers. Similarly, if we add 1.5 x IQR to the third quartile, any data values that are greater than this number are considered outliers.

**What numbers are considered outliers?**A commonly used rule says that a data point is an outlier if it is

**more than 1.5 ⋅ IQR 1.5cdot textIQR 1.**

**5⋅IQR1**, point, 5, dot, start text, I, Q, R, end text above the third quartile or below the first quartile. Said differently, low outliers are below Q 1 − 1.5 ⋅ IQR textQ_1-1.5cdottextIQR Q1−1.

**What is the 1.5 IQR rule?**

Add **1.5 x (IQR) to the third quartile**. Any number greater than this is a suspected outlier. Subtract 1.5 x (IQR) from the first quartile. Any number less than this is a suspected outlier.

**What is considered an outlier in statistics standard deviation?**

**If a value is a certain number of standard deviations away from the mean, that data point** is identified as an outlier. The specified number of standard deviations is called the threshold. … The more extreme the outlier, the more the standard deviation is affected.

### What does having no outliers mean?

There are no outliers. Explanation: **An observation** is an outlier if it falls more than above the upper quartile or more than below the lower quartile. … The minimum value is so there are no outliers in the low end of the distribution. You may also read,

### What does outlier mean in math terms?

An outlier is **a number that is at least 2 standard deviations away from the mean**. For example, in the set, 1,1,1,1,1,1,1,7, 7 would be the outlier. Check the answer of

### Can you have a negative outlier?

More on IQR and Outliers: … – If our range has a natural restriction, (like it can’t possibly be negative), it’s okay for an outlier limit to be beyond that restriction. – If a value is more than **Q3 + 3*IQR or less than Q1 –** 3*IQR it is sometimes called an extreme outlier.

### What can IQR tell us?

The interquartile range (IQR) is the distance between the first and third quartile marks. The IQR is a measurement of the variability about the median. More specifically, the IQR tells **us the range of the middle half of the data**. Read:

### What if lower fence is negative?

Yes, a lower inner fence can be negative even **when all the data are strictly positive**. If the data are all positive, then the whisker itself must be positive (since whiskers are only at data values), but the inner fences can extend beyond the data.

### What is the two standard deviation rule for outliers?

Z-scores are the number of standard deviations above and below the mean that each value falls. For example, **a Z-score of 2 indicates** that an observation is two standard deviations above the average while a Z-score of -2 signifies it is two standard deviations below the mean.

### What is the 2 standard deviation rule?

Under this rule, 68% of the data falls within one standard deviation, **95% percent within two standard deviations**, and 99.7% within three standard deviations from the mean.

### What is another word for outlier?

2 **nonconformist**, maverick; original, eccentric, bohemian; dissident, dissenter, iconoclast, heretic; outsider.

### Why is the mean most affected by outliers?

The **outlier decreases the mean** so that the mean is a bit too low to be a representative measure of this student’s typical performance. This makes sense because when we calculate the mean, we first add the scores together, then divide by the number of scores. Every score therefore affects the mean.

### Do outliers affect the mean?

Outliers affect **the mean value of the data** but have little effect on the median or mode of a given set of data.