# Why do we use log transformation?

When our initial continuous data does not follow the bell curve, we may log convert it to make it as "normal" as feasible, increasing the validity of the statistical analysis results. To put it another way, the log transformation decreases or eliminates the skewness of our original data. When there is no skew, it is easier to analyze using statistics.

The most common reason for using the log transformation is when our data are counts or frequencies, such as the number of times something happens. For example, if we were looking at the number of times animals on a farm got kicked out of their pen, this would be a count data set and applying the log transformation to it would make the data more normal. The log transformation allows us to calculate probabilities from counts by using the formula P(event) = e^(-x), where x is the log of the probability. If we can't use probabilities, such as with non-randomly sampled data, then we need some other method. For example, if half of all cows kicked out of their pen died within one year, this would not be able to be estimated using probabilities.

Another example would be when our data are measurements taken on individual objects, such as weights of fish. We usually take several measurements on each object, which are called replicates. For example, let's say I measure the weight of 10 fish and they average 10 ounces each.

## Why do we transform?

Transforms are typically used to make data appear to more closely match the assumptions of a statistical inference technique, or to improve the interpretability or look of graphs. The function used to convert the data is almost always invertible and, in general, continuous. Thus, all transforms can be viewed as methods for changing the shape of data without changing their relative positions.

Some common reasons for transforming data include: adjusting it so that it has a (approximately) normal distribution; making its range easier to understand; removing outlying values; and reducing variance within the data. Transforming data in these ways can help with many problems in statistics and machine learning, including bias-variance tradeoffs, better model fitting, and improving prediction accuracy.

There are many different transforms available. Some common ones include the logarithmic, square root, and power transformation. Each changes the shape of the data in its own way while keeping the relationship between pairs of observations intact. There are also inverse transformations, which will recover the original data given an image of it under a transform.

In practice, there are two main approaches for applying transforms: direct and indirect. With direct transforms, the operator directly applies the transform to each value in the dataset before passing it on to other functions. This is the approach used by the stat command when applying the logarithmic or square root transformation to numeric variables.

## What is the log2 transformation?

In lumi, the ssn (simple scaling normalization) approach is the log2-median transformation. It multiplies the non-logged expression value by the ratio of the column (sample) median to the mean of all sample medians. This results in values that can be directly compared to quantitative measurements like DNA or RNA amounts.

## What do you do when the log is negative?

A popular method for dealing with negative numbers is to pre-process the data with a constant value before performing the log transform. As a result, the transformation is log (Y+a), where an is a constant. Some individuals like to select a such that min (Y+a) is a very tiny positive value (like 0.001). Others select a such that min (Y + a) = 1. Either way, this procedure ensures that there are no negative values after applying the log transform.

## Why should we use logs?

Logarithmic scales are used in charts and graphs for two reasons. The first is to respond to skewness towards large values, which occurs when one or a few points are significantly larger than the majority of the data. The second option is to display percentage changes or multiplicative factors. Logarithms convert small differences into proportionate ones, making it easier to compare quantities that may not be equal.

For example, if you wanted to know how much more money you would have if your income doubled, you could calculate this by taking the log of each side of the equation and solving for the log of \$100,000. The answer is about 10.3, which can be entered into an exponential calculator to obtain the exact amount you would have (\$1023.68).

This method avoids comparing numbers that may not be equal and ensures that even very large increases or decreases in income are displayed in a relative way.

The doubling of your income was so significant that it required a new chart of accounts. Your old one wouldn't be able to reflect this change because it was set up with your previous income levels. However, using logs allows us to view these increased amounts without overflowing the scale.

We also use logs in charts that show percentage changes over time.

## What is the purpose of log transformation in image processing?

Try looking at a log-shaped graph with input intensities on the x axis and output (result) intensities on the y axis. You'll receive different results depending on whether you use a log or inverse log transform. Lower intensities are mapped/changed/transformed to higher intensities using the log transform. Conversely, higher intensities are mapped to lower values using the inverse log transform.

When working with images, we often want to apply mathematical operations to each pixel in the image. For example, we might want to calculate the average, maximum, or minimum value within an image. We can do this by applying a function to each element in the array representing the image. There are many functions that could be used for this purpose, but one common choice is the log transform. The reason for this choice is that low intensity values represent rare events so their contribution toward the overall mean or median will be small. By transforming the data into "magnitudes", these rare events are made visible, allowing us to take them into account when calculating the final result.

There are two main types of transforms that can be applied to arrays: linear and non-linear. The log transform is a non-linear operation because it maps positive numbers to larger values and negative numbers to smaller values.

## What does "transformation" mean to you?

A transformation is a significant change in shape or appearance. A significant event in your life, such as acquiring your driver's license, attending college, or marrying, might result in a life shift. A metamorphosis is a drastic and profound shift. A revolution is a major turning point that creates a new situation.

Your body is undergoing many changes as it transforms from one stage of life to another. At each stage, your body is growing and developing differently. For example, when you are born, you are completely free of any illness or injury and are able to breathe without help from others. After about one year, your body begins to change as it develops muscles and learns how to walk.

As you can see, your body goes through many changes as it transforms from one stage of life to another. The word "transformation" may make you think only of big changes like those mentioned above, but it also describes small changes that occur regularly, such as the bones in your face changing shape due to stress and strain over time. New cells are constantly being made throughout your life; some replace old damaged cells while others build new organs. All of this growth and development is called "natural aging" because there is nothing you can do to stop it from happening.

However, there are things you can do to maintain your health as you transform from one stage of life to another.

#### About Article Author

##### Mary Ramer

Mary Ramer is a professor in the field of Mathematics. She has a PhD in mathematics, and she loves teaching her students about the beauty of math. Mary enjoys reading all kinds of books on math, because it helps her come up with new interesting ways how to teach her students.

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