Did You Know?

Represented by the letter 'r', the most common measure of correlation is the Pearson Product Moment Correlation.

A correlation is a kind of relationship between two variables such that if one undergoes a change, the other does as well. This is somewhat similar with what we call the proportion theory in math―direct and indirect proportion. If the value of variable x increases/decreases and the value of y increases/decreases as well, x and y are said to be directly proportional.Represented by the letter 'r', the most common measure of correlation is the Pearson Product Moment Correlation.

Conversely, if the value of x increases/decreases and the value of y decreases/increases, x and y are said to be inversely proportional to each other. In statistics, the concept of correlation defines a similar relationship between constantly changing variables. There are three types of correlation: zero, positive, and negative. The paragraphs below will explain what a negative correlation is, along with examples.

The Concept

- When two variables have no relationship, it indicates zero correlation.
- When the value of one variable increases/decreases simultaneously with the other, it indicates a positive correlation, that is to say, they are positively related to each other.
- The definition of negative correlation states that it is a relationship between two variables, such that when the value of one variable increases, the value of the other decreases and vice versa.
- It is akin to the concept of inverse proportion. The variables are negatively related to each other.
- In statistical studies, a perfect negative correlation can be expressed as -1.00, a perfect positive correlation can be expressed by +1.00, and a zero correlation is expressed as 0.00.
- The concept of negative correlation can be explained clearly by means of a scatterplot, as shown below.

- In the above diagram, you can see that the variables are grades and absenteeism. That is to say, the more the absenteeism, lesser the grades.
- At (60, 40), it indicates that 60% of absence in class will lead to 40% reduction in grades. Similarly, at (80, 20), it indicates 20% grades for 80% absenteeism.

In Psychology

- To understand why and how the above concept seems to be related to psychology, you need to understand correlational studies, which are often used as a measure to find out the relationship between variables in psychology.
- That is to say, when trying to analyze instances from a psychological perspective, it is essential to find out units of measurement related to the individuals/situation, perform a comparative study among a group of individuals, and come up with suitable inferences.
- So, when you deal with a situation, you first understand and classify the variables. Then, you have to collect data and observe and detect patterns.
- Post this step, you will be able to conclude and establish what kind of relationship they share.
- Consider an example for negative correlation. Let's say, a comparative study is being done among a group of individuals who consume alcohol.
- From this group, there will be people who drink very little to those who consume a lot per day. This will be your first variable―the amount of alcohol consumed.
- For the second variable, you may consider the health factor of these individuals―the heart, liver, etc.
- Of course, this may be a very random assumption; after all, every one handles the effect of alcohol according to their drinking habits and body constitution, and other factors play a major part in determining health as well.
- As you note down the data and compare them, you may notice that more the alcohol consumed, less healthy the individual is. Conversely, the lesser the alcohol consumption, the healthier the individual is. This is what negative correlation is.
- This may be true for all individuals or a select few. If the former is true, it is an example of perfect negative relationship (-1.00).
- If the latter is true, the variables may be weakly or moderately in a negative relationship.
- A value of -0.20 to - 0.29 indicates a weak negative relationship. A value of -0.30 to -0.39 indicates a moderate negative relationship.
- Two variables are said to have a strong negative relationship if the correlation value is between -0.40 to -0.69. And, a value between -0.70 to -0.99 indicates a very strong negative relationship.

Examples

Example I

The weight of a car and miles per gallon.

If a car is very heavy, you will observe that it travels miles for every gallon of gas. If it is lightweight, it can cover more distance per gallon. It is one of the most practical examples of negative correlation in real life.

If a car is very heavy, you will observe that it travels miles for every gallon of gas. If it is lightweight, it can cover more distance per gallon. It is one of the most practical examples of negative correlation in real life.

Example II

More absenteeism in school activities, less GPA.

You GPA depends not only on your academic excellence, but also on your involvement in extra-curricular activities. If you tend to remain absent from these activities, you will lose out on a lot of extra credits. Thus, the more absenteeism from school activities, the lesser your GPA will be.

You GPA depends not only on your academic excellence, but also on your involvement in extra-curricular activities. If you tend to remain absent from these activities, you will lose out on a lot of extra credits. Thus, the more absenteeism from school activities, the lesser your GPA will be.

Example III

More vaccinations, less illness.

The more you are vaccinated for a disease, the lesser your chances are of procuring the same.

The more you are vaccinated for a disease, the lesser your chances are of procuring the same.

Example IV

Increase in height, decrease in temperature.

You may have noticed this quite often. There is a negative relationship between temperature and sea level. As you go above the sea level, say you drive on a steep mountain path or climb a hill, you will notice that the air keeps thinning and the temperature lowers as you go higher and a higher.

You may have noticed this quite often. There is a negative relationship between temperature and sea level. As you go above the sea level, say you drive on a steep mountain path or climb a hill, you will notice that the air keeps thinning and the temperature lowers as you go higher and a higher.

Example V

Pacifying a child with the wrong method.

New parents may have experienced many instances of correlation. An example of negative correlation would be when they try to soothe their cranky kid with music. In this case, the variables are the song and the baby's calm behavior. They may notice that the more they play a particular song or any kind of music, the kid behaves less and less calmer, thus indicating a negative relationship.

New parents may have experienced many instances of correlation. An example of negative correlation would be when they try to soothe their cranky kid with music. In this case, the variables are the song and the baby's calm behavior. They may notice that the more they play a particular song or any kind of music, the kid behaves less and less calmer, thus indicating a negative relationship.

Example VI

More expenditure, less money.

This is a rather obvious instance. The more money you spend on something―shopping, bills, etc.―the lesser money you have in your pocket.

This is a rather obvious instance. The more money you spend on something―shopping, bills, etc.―the lesser money you have in your pocket.

Example VII

More time for fun, less grades.

The more number of hours a student puts in for fun activities like watching television, playing video games, etc., the lesser his grades will be.

The more number of hours a student puts in for fun activities like watching television, playing video games, etc., the lesser his grades will be.

Example VIII

More time at work, less time at home.

As you spend more and more time at your workplace, it becomes difficult to spend that much time at home Consequently, the more time you spend at office, the lesser time you give to your family.

As you spend more and more time at your workplace, it becomes difficult to spend that much time at home Consequently, the more time you spend at office, the lesser time you give to your family.

Example IX

Higher expense ratio, less returns.

If you have made invested in mutual funds, you may have noticed that the higher your expense ratio is, the lesser are your investment returns.

If you have made invested in mutual funds, you may have noticed that the higher your expense ratio is, the lesser are your investment returns.

The concept of correlation is widely used by researchers to detect patterns and associations in psychology. Quite often, it is possible that two variables may be negatively correlated in some cases, but not all.