## P

### Parameter

A value which describes a population.

### Parametric criteria

Data should be:

- Normally distributed
- Variances should be similar (the standard deviation of the most-variable sample should be less than 10 times the standard deviation of the least-variable sample).

### Pearson correlation coefficient

Parametric test for the significance of the linear relationship between two variables.

### Percentage

A proportion expressed as a value relative to one hundred (e.g. three-quarters = 0.75 = 75%).

### Population

The entire set of individuals / items of relevance to a research question.

### Population size (n)

The number of individuals / items in a population.

### Prediction

A statement of what pattern in data is expected if research hypothesis is true.

### Probability

A measure of the likelihood of an event or result. For instance, for a dice there is a probability of one in six that a particular face will turn up on a given through - usually written as p = 0.16666. Results of statistical tests are usually expressed relative to a critical significance level, for instance P < 0.05 indicates that the null hypothesis has been rejected on the basis that the pattern observations had a probability of less than one in twenty of occurring by chance.

### Proportion

One value expressed relative to a second value, for example a fraction (see also percentage).