Research methods Key Terms

Normal distribution

A continuous probability distribution that is symmetrical around its mean, with the characteristic bell‑shaped curve.

Skewed distribution

A distribution that is asymmetrical, with a longer tail on one side, indicating that the mean and median are not equal.

Correlation coefficient

A statistical index (r) that measures the strength and direction of a linear relationship between two continuous variables, ranging from -1 to +1.

Statistical significance

A determination that a result (e.g., a correlation) is unlikely to be due to random sampling error, typically assessed using a p‑value and a pre‑set alpha level.

Nominal scale

A measurement scale that categorises data without any inherent order, such as gender or nationality.

Ordinal scale

A measurement scale that orders data but does not guarantee equal intervals between ranks, such as a 5‑point Likert scale.

Coding scheme

A structured list of codes and accompanying definitions that guide the systematic classification of data in content analysis.

Inter‑coder reliability

A statistical measure of agreement between two or more coders who independently apply codes to the same data set.

Statistical testing

A set of procedures used to determine whether observed data provide sufficient evidence to reject a null hypothesis in favour of an alternative hypothesis.

p‑value

The probability, calculated from the data, of obtaining a test statistic as extreme as, or more extreme than, the one observed, assuming the null hypothesis is true.

Sign test

A non‑parametric test that assesses whether the median of paired differences is zero by counting the number of positive and negative signs.

Median

The middle value of a distribution when data are arranged in ascending order; in the sign test it is the parameter of interest.

Critical value

The threshold value from a statistical distribution that determines whether a test statistic is significant.

p‑value

The probability of observing data as extreme as, or more extreme than, the actual data, assuming the null hypothesis is true.

Type I error

An error where a true null hypothesis is incorrectly rejected, producing a false positive result.

Type II error

An error where a false null hypothesis is not rejected, producing a false negative result.

Level of measurement

The scale that describes the nature of the information contained in the variable, determining which statistical tests are appropriate.

Inferential test

A statistical procedure that uses sample data to make conclusions about a population, such as t‑tests, chi‑square tests, ANOVA, and correlation.

Inferential statistics

Statistical methods that allow researchers to draw conclusions about a population based on sample data, including hypothesis testing and confidence intervals.

Between‑subjects design

An experimental design in which different participants are assigned to each level of the independent variable, ensuring that each participant experiences only one condition.

Pearson's r

A parametric measure of linear correlation between two continuous variables, assuming normal distribution.

Mann‑Whitney U test

A non‑parametric test for comparing two independent samples when data are ordinal or not normally distributed.