Sampling Methods, Data Descriptions, and Correlational Research in Psychology

Sampling

The process of selecting a subset of individuals from a population to estimate characteristics of the whole population.

The myth of random sampling

Most behavioral research does not use random samples due to reasons such as impossibility, expense, and impracticality.

Probability sample

Necessary when researchers are trying to estimate the number of people in a population who display certain attitudes, behaviors, or problems.

Error of estimation

The degree to which the data obtained from the sample are expected to deviate from the population as a whole.

Simple random sample

A sample in which every possible sample of the desired size has the same chance of being picked.

Ex: random number generator

An example of a method used to create a simple random sample.

Systematic sample

Individuals are chosen systematically, such as through gym class numbering for teams.

Stratified random sample

Population divided into groups, from which samples are taken.

Cluster sampling

Population divided into clusters, with some whole clusters randomly selected; not probability-based as it lacks a sampling frame.

Response rates and bias

Factors affecting response rates include literacy, lack of time, inconvenient timing, illness, disinterest, suspicion, and misgeneralization.

Nonresponse

Failure to obtain responses from individuals selected for a sample.

Nonprobability sample

A sample that does not involve random selection, often based on convenience.

Convenience sample

Participants that are readily available for the study.

Quota sample

A convenience sample in which the researcher ensures that certain kinds of participants are obtained in particular proportions.

Purposive sample

Researchers use past research findings or their judgment to decide which participants to include in the sample, aiming for typical respondents.

Sample size

Larger sample sizes lead to greater statistical power.

Power

The ability of a research design to detect effects of the variables being studied that exist in the data.

Descriptive research

Research that describes characteristics of a population or phenomenon being studied.

Survey

A method of collecting data through questionnaires, interviews, or observations.

Cross-sectional survey

A survey where a single group is interviewed at one point in time.

Successive Independent survey

A survey conducted at the same time frame but with different groups interviewed.

Longitudinal/panel survey

A survey where a single group is surveyed over time.

Demographic

Describes patterns of basic life events and experiences such as birth, marriage, divorce, employment, migration, and death.

Epidemiological

Describes the occurrence of disease and death in different groups of people.

Criteria

Accuracy, Concise, Understandable.

Methods

Numerical - numbers, percentages; Graphical - graphs, figures.

Simple frequency distribution

Summarizes raw data by showing the number of scores that fall in each of several categories.

Grouped frequency distribution

Data are broken into several subsets or class intervals of equal size → frequency within each is indicated.

Histograms

Show frequency.

Measures of central tendency

Mean, median, mode.

Confidence intervals

An estimation of the range within which the population mean falls.

Error bars

Represent researcher's confidence in the value of each mean.

Range

Difference between the highest and lowest scores.

Variance

Index of the average amount of variability in a set of data, expressed in square units.

Standard deviation

Square root of the variance.

Normal distribution

Bell curve.

Skewed distribution

Data distribution is non-normal.

Z-scores

How a particular participant's score compares to the rest of the data.

Correlational research

Describe the relationship between two or more variables.

Correlation coefficient (r)

Represents the strength and direction of the relationship between two variables.

Positive correlation

Both variables increase.

Negative correlation

One variable increases as the other decreases.

Magnitude of the correlation coefficient

The numerical value, ignoring the sign, expresses the strength of the relationship.

Coefficient of determination

r^2; Proportion of the variance in one variable that is explained or accounted for by the other variable.

Correlation does not imply causation

Indicates that correlation between two variables does not mean that one causes the other.