Distribution Psychology

Distribution Psychology Definition

When researchers collect data, the majority of the time, researchers aim to use statistical tests to empirically test if their data findings support or reject the hypotheses they proposed at the start of the study.

However, there are two types of parametric tests:

1. Parametric tests
2. Nonparametric tests

But how do researchers know when to use which test? One of the answers is distribution. When data has a normal distribution, a parametric test is used, and data with skewed distributions use nonparametric tests.

Now that we've figured out the uses of distributions in psychology let's understand what the data analysis method means.

Characteristics of Distribution

Distribution graphs have numerous names, such as the bell curve graph or Gaussian distribution graph. Let's take a look at the characteristics of a distribution graph:

• Shape - The distribution graphs should resemble a bell with its tail extending to each side of the chart. The highest point of the graph is where there is the highest likelihood of the phenomenon occurring.

• Central tendency - The mean, median and mode are important figures used to understand and interpret distribution graphs. The graph can be used to identify how much each value differs from the average. The mean, median and mode values are usually the same in a normally distributed graph.

• Variability - From distribution graphs, researchers can calculate how much each data point varies from the average.

Types of Distributions in Psychology

Now that we know what distributions mean let's look at the different types and how we can identify them.

• Normal distribution - the graph resembles a bell shape; the highest point of the chart should be at the centre of the chart, the left and right-hand sides of the graph should be symmetrical, and the tail should extend to each side of the graph.

• Positively skewed distribution - the mean, median and mode of distribution are positive, so the graph has a long tail extending to the right, and the highest point of the graph is shifted to the left.

• Negatively skewed distribution - the mean, median and mode of distribution are negative, so the graph has a long tail extending to the left, and the highest point of the graph is shifted to the right.

Frequency Distribution Psychology

In psychology, distributions can mean many things. The types of distribution we are focusing on are based on probability. However, frequency distributions are used to understand data. For instance, how often something is observed.

Imagine a research project investigating 100 people of various ages. The researcher can't understand how common specific ages are by looking at each case. Instead, the data is organised using frequency distribution.

An example of how frequency distributions in psychology may look is shown in the table below.

Frequency distributions are related to the probability distribution. From frequency distributions, the researcher can identify outliers and whether the data centres around the averages (central tendency values); these factors contribute to whether data is normally distributed.

Normal Distribution

Let's look at what a normal distribution graph looks like to interpret what the graph shows.

Figure 1 - Graph depicting a normal distribution.

The graph shows that the highest point of the curve is in the middle of the graph, and both sides of the chart are symmetrical. But what does it mean?

The mean, median and mode are the same, as the distribution is symmetrical half of the scores are above the average, and the other half are below the average. The mean is equal to 0, and the standard deviation to 1.

In normal distributions:

• 99.7% of observations fall within + or - 3 SD of the mean.
• 95.4 of observations fall within + or - 2 SD of the mean.
• 68.2% of observations fall within + or - 1 SD of the mean.

A smaller SD means that the data is less varied, so the data is less likely to have outliers affecting the reliability and validity of findings.

Example of Normal Distribution in Psychology

Suppose in a psychology test. These were the average results of the class:

These findings suggest a normal distribution because the mean, median, and mode are approximately the same. And so, if this were plotted onto a graph, it would probably take the shape of a bell curve.

When the mean, median and mode are approximately the same, then this suggests that the dataset does not have many outliers.

Skewed Distribution Psychology

The two types of skewed distribution charts we will cover are positive and negative.

Figure 2 - Examples of a negative and positive skewed distribution graph.

Let's start by understanding negatively skewed charts.

Typically the scores will mostly be larger numbers and fewer smaller figures. And the mean will fall to the left of the median, which will cause the tail to extend to the left. The data is skewed when all of the central tendency values are not equal to 0.

On the other hand, positively skewed data is the opposite. The majority of the numbers will be smaller rather than larger. The mean will fall to the median's right, causing the graph's tail to extend to the right. The findings would suggest a lower probability of occurrence of the phenomenon investigated.

Positively Skewed Distribution and Negatively Skewed Distribution Examples

Let's take a look at an example of a positively skewed distribution graph average data output:

The mode and median are below the mean.

What about these results?

These suggest a negative skew since most people scored high as the mode and median are higher here.

Do these results indicate anything?

If we look at the examples above, the positively skewed shape indicates that the participants scored lower on average, so perhaps the test was too hard. Similarly, the negatively skewed graph shows higher scores, so maybe the test was too easy. The mode is the highest point that illustrates the distribution.

We can then suggest making the test harder or easier, depending on the distributions above.