What is an outlier in analytical chemistry?

Asked By: Hasnae Ingrassia | Last Updated: 15th February, 2020
Category: technology and computing databases
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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.

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Subsequently, one may also ask, what is an outlier in chemistry?

Outliers are defined as observations that appear to be inconsistent with the rest of the data set. A given data set can have more than one outlier, though it is rare in the laboratory setting.

Beside above, should I remove outliers? If the outlier does not change the results but does affect assumptions, you may drop the outlier. If the outlier creates a significant association, you should drop the outlier and should not report any significance from your analysis.

Also know, what is Q test in analytical chemistry?

Dixon's Q test, or just the “Q Test” is a way to find outliers in very small, normally distributed, data sets. It's commonly used in chemistry, where data sets sometimes include one suspect observation that's much lower or much higher than the other values.

What is another word for outlier?

Words related to outlier aberration, deviation, oddity, eccentricity, exception, quirk, anomaly, deviance, irregularity, outsider, nonconformist, maverick, original, eccentric, bohemian, dissident, dissenter, iconoclast, heretic.

34 Related Question Answers Found

How are quartiles calculated?

Quartiles are the values that divide a list of numbers into quarters: Put the list of numbers in order. Then cut the list into four equal parts.

In this case all the quartiles are between numbers:
  1. Quartile 1 (Q1) = (4+4)/2 = 4.
  2. Quartile 2 (Q2) = (10+11)/2 = 10.5.
  3. Quartile 3 (Q3) = (14+16)/2 = 15.

What impact would an outlier have?

An outlier is a value that is very different from the other data in your data set. This can skew your results. As you can see, having outliers often has a significant effect on your mean and standard deviation. Because of this, we must take steps to remove outliers from our data sets.

How do you identify outliers in statistics?

The IQR defines the middle 50% of the data, or the body of the data. The IQR can be used to identify outliers by defining limits on the sample values that are a factor k of the IQR below the 25th percentile or above the 75th percentile. The common value for the factor k is the value 1.5.

What is an outlier person?

An “outlier” is anyone or anything that lies far outside the normal range. In business, an outlier is a person dramatically more or less successful than the majority. Do you want to be an outlier on the upper end of financial success? Gladwell attempts to get to the bottom of what makes a person successful.

Can lower fence be negative?


1 Answer. 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.

Why is 1.5 IQR rule?

Using the Interquartile Rule to Find Outliers
Multiply the interquartile range (IQR) by 1.5 (a constant used to discern outliers). Add 1.5 x (IQR) to the third quartile. Any number greater than this is a suspected outlier.

What does Iqr mean?

The interquartile range (IQR) is a measure of variability, based on dividing a data set into quartiles. Quartiles divide a rank-ordered data set into four equal parts. The values that divide each part are called the first, second, and third quartiles; and they are denoted by Q1, Q2, and Q3, respectively.

What does an outlier look like on a Boxplot?

An outlier is an observation that is numerically distant from the rest of the data. When reviewing a boxplot, an outlier is defined as a data point that is located outside the fences (“whiskers”) of the boxplot (e.g: outside 1.5 times the interquartile range above the upper quartile and bellow the lower quartile).

What is considered an outlier in statistics?

In statistics, an outlier is a data point that differs significantly from other observations. An outlier may be due to variability in the measurement or it may indicate experimental error; the latter are sometimes excluded from the data set. An outlier can cause serious problems in statistical analyses.

What is considered an outlier in a normal distribution?


One definition of outliers is data that are more than 1.5 times the inter-quartile range before Q1 or after Q3. Since the quartiles for the standard normal distribution are +/-. 67, the IQR = 1.34, hence 1.5 times 1.34 = 2.01, and outliers are less than -2.68 or greater than 2.68.

What z score is an outlier?

Any z-score greater than 3 or less than -3 is considered to be an outlier. This rule of thumb is based on the empirical rule. From this rule we see that almost all of the data (99.7%) should be within three standard deviations from the mean.

Which data set has an outlier?

One definition of outlier is any data point more than 1.5 interquartile ranges IQRs below the first quartile or above the third quartile. The interquartile range IQR is the difference between the third quartile and the first quartile of the data set.

How do you get rid of outliers?

To determine whether data contains an outlier:
  1. Identify the point furthest from the mean of the data.
  2. Determine whether that point is further than 1.5*IQR away from the mean.
  3. If so, that point is an outlier and should be eliminated from the data resulting in a new set of data.

How do you find outliers in a scatter plot?

If one point of a scatter plot is farther from the regression line than some other point, then the scatter plot has at least one outlier. If a number of points are the same farthest distance from the regression line, then all these points are outliers.

What is T test used for?


A t-test is a type of inferential statistic used to determine if there is a significant difference between the means of two groups, which may be related in certain features.

How is Q value calculated?

Thus the Q-value equation is literally the expected false positives based on the P-value, divided by the total number of positives actually accepted at that same P-value. You can use the Q-value much like a P-value. For example, you might choose to accept all results with a Q-value of 0.25 or less.

What is the formula for confidence interval?

For a population with unknown mean and known standard deviation , a confidence interval for the population mean, based on a simple random sample (SRS) of size n, is + z* , where z* is the upper (1-C)/2 critical value for the standard normal distribution.