Relationship between two variables psychology

Psychological Statistics

relationship between two variables psychology

Correlation means that there is a relationship between two or more variables ( such as ice cream consumption and crime), but this relationship does not. Random Sample in Psychology: Example & Definition. Random Assignment . It means that two variables have a relationship between them. Psychologists are not alone in their use of correlations, in fact many disciplines will The relationship between two variables will always produce a coefficient of .

In a negative relationship the variables tend to move in the opposite directions: If one variable increases, the other tends to decrease, and vice-versa. The direction of the relationship between two variables is identified by the sign of the correlation coefficient for the variables. Postive relationships have a "plus" sign, whereas negative relationships have a "minus" sign.

The Form Shape of a Relationship: The form or shape of a relationship refers to whether the relationship is straight or curved. A straight relationship is called linear, because it approximates a straight line.

A curved relationship is called curvilinear, because it approximates a curved line. An example of the relationship between the Miles-per-gallon and engine displacement of various automobiles sold in the USA in is shown below.

relationship between two variables psychology

This is curvilinear and negative. In this course we only deal with correlation coefficients that measure linear relationship. There are other correlation coefficients that measure curvilinear relationship, but they are beyond the introductory level.

The Degree Strength of a Relationship Finally, a correlation coefficient measures the degree strength of the relationship between two variables.

The mesures we discuss only measure the strength of the linear relationship between two variables. Two specific strengths are: They are said to be perfectly linearly related, either positively or negatively.


When two variables have no relationship at all, their correlation is 0. Taking all the points into account, one can see that people under more stress tend to have more physical symptoms.

There is a negative relationship between stress and immune system functioning, for example, because higher stress is associated with lower immune system functioning. The circled point represents a person whose stress score was 10 and who had three physical symptoms.

A value of 0 means there is no relationship between the two variables. With the exception of reliability coefficients, most correlations that we find in Psychology are small or moderate in size. It is not a good measure for nonlinear relationships, in which the points are better approximated by a curved line.

Those who get too little sleep and those who get too much sleep tend to be more depressed. Even though Figure 6. Nonlinear relationships are fairly common in psychology, but measuring their strength is beyond the scope of this book.

Positive Correlation in Psychology: Examples & Definition - Video & Lesson Transcript |

It is a good idea, therefore, to design studies to avoid restriction of range. For example, if age is one of your primary variables, then you can plan to collect data from people of a wide range of ages. It seems clear, however, that this does not mean that eating chocolate causes people to win Nobel prizes, and it would not make sense to try to increase the number of Nobel prizes won by recommending that parents feed their children more chocolate.

There are two reasons that correlation does not imply causation. Consider, for example, a study showing that whether or not people exercise is statistically related to how happy they are—such that people who exercise are happier on average than people who do not. This statistical relationship is consistent with the idea that exercising causes happiness, but it is also consistent with the idea that happiness causes exercise. Perhaps being happy gives people more energy or leads them to seek opportunities to socialize with others by going to the gym.

For example, the fact that nations that have won more Nobel prizes tend to have higher chocolate consumption probably reflects geography in that European countries tend to have higher rates of per capita chocolate consumption and invest more in education and technology once again, per capita than many other countries in the world.

Correlational research for A level psychology - Psychteacher

Similarly, the statistical relationship between exercise and happiness could mean that some third variable, such as physical health, causes both of the others. Being physically healthy could cause people to exercise and cause them to be happier. Some excellent and funny examples of spurious correlations can be found at http: One website about correlation and causation, http: Many of the headlines suggest that a causal relationship has been demonstrated when a careful reading of the articles shows that it has not because of the directionality and third-variable problems.

One such article is about a study showing that children who ate candy every day were more likely than other children to be arrested for a violent offense later in life. What alternative explanations can you think of for this statistical relationship?

It could be that children who revise more have more stable home lives, and the more stable home life could mean they do more homework and pay more attention at school, which in turn could lead to higher grades in exams.

It is very difficult to establish cause and effect. Correlations can be misused. As finding a correlation between two variables tells us very little other than that a relationship exists, it is very difficult to make accurate conclusions about the causes of the relationship.

Media, governments, and even sometimes scientists often make wild claims based on correlations that sound convincing to the public and support an argument, but in reality the relationship could mean something completely different.

relationship between two variables psychology

It is essential to read the title and descriptions of the axis so that you know what variables the graph is describing. You must then decide whether the correlation is positive or negative.

relationship between two variables psychology

The question may also ask for one strength or one weakness of correlations, and to answer you should describe one of each and relate it to the topic the graph is describing.

You must then describe the relationship in the graph you have been given. One weakness is that cause and effect cannot be established because correlations do not equal causation and there may be another mediating variable.

relationship between two variables psychology

For example, children who spend more hours in day care may have less caring mothers, and so the children may react aggressively in order to get attention. Maternal sensitivity is the mediating variable.