Week 1 - Essential theory and SPSS

What determines the choice of statistical test in psychology research?

Scale of measurement, research aims (descriptive, relational, experimental), experimental design, and distribution of the dependent variable.

What is the difference between parametric and non-parametric statistics?

Parametric tests assume normally distributed data; non-parametric tests are used when data is not normally distributed.

What is a nominal scale?

A scale where numbers or names serve as labels with no numerical relationship (e.g., gender, religion).

What is an ordinal scale?

A scale that ranks data with meaningful order, but intervals between ranks may not be equal (e.g., race position).

What is an interval scale?

A scale with equal intervals between values but no true zero (e.g., temperature in ºF).

What is a ratio scale?

A scale with equal intervals and a true zero point (e.g., height, weight).

What are the three main research aims in psychology statistics?

Descriptive (summarize data), relational (explore relationships), and experimental (test differences).

When is the mean an appropriate measure of central tendency?

When data is continuous or discrete and normally distributed.

When should the median be used instead of the mean?

When data is continuous or discrete but not normally distributed.

What measure of central tendency is used for categorical data?

Mode.

What are common measures of spread in descriptive statistics?

Standard deviation and range.

What is the goal of relational research?

To explore relationships between variables without manipulation, allowing prediction but not causality.

What is the goal of experimental research?

To examine the influence of IVs on DVs and infer causality if confounding variables are controlled.

What is a true experimental design?

A design where IVs are actively manipulated and random allocation is possible.

What is a quasi-experimental design?

A design where IVs reflect fixed characteristics and random allocation is not possible.

What is a between-subjects design?

Participants are exposed to only one level of the IV.

What is a within-subjects design?

Participants are exposed to all levels of the IV.

What is a mixed design in experiments?

At least one IV is between-subjects and one is within-subjects.

What are the properties of a normal distribution?

Symmetrical, bell-shaped, centered around the mean.

What is kurtosis and what do its types indicate?

Kurtosis measures the "tailedness" of a distribution

What does skewness indicate in a distribution?

The asymmetry of the distribution

What is a z-score and how is it calculated?

A standardized score calculated as z = (X - μ) / σ.

What does the standard normal distribution tell us?

It shows the proportion of scores within standard deviations from the mean (e.g., 95% within ±1.96 SD).

What is a sampling distribution?

The distribution of a statistic (e.g., mean) across infinite samples; it is normally distributed.

What is the standard error (SE)?

The standard deviation of the sampling distribution; it decreases with larger sample sizes.

What is the estimated standard error (ESE)?

An estimate of SE based on sample data when population parameters are unknown.

How is a 95% confidence interval around a sample mean calculated?

CI = X̄ ± t₀.₉₇₅ × ESE.

Why is the t-distribution used instead of the z-distribution?

Because population parameters are usually unknown and sample sizes are limited.

What is the null hypothesis (H₀)?

The assumption that there is no difference between population means.

What does a p-value represent in hypothesis testing?

The probability of observing the data if the null hypothesis is true.

What are Type I and Type II errors?

Type I