Stats 241 Week 1

Observational study

A study where researchers observe what happens without assigning treatments or influencing subjects.

Experimental study

A study where researchers actively assign treatments to subjects to study cause-and-effect.

Comparitive study

A study that compares two or more groups to see differences in outcomes.

Descriptive study

A study that describes characteristics of a population or phenomenon without making comparisons or testing causation.

Explanatory variable

The variable that explains or influences changes in another variable (independent variable).

Response variable

The variable that is measured to see the effect of the explanatory variable (dependent variable).

Treatment

The conditions applied to experimental units (e.g., different drugs or doses).

Experimental units

The smallest units that receive a treatment (e.g., a person, plant, or plot of land).

Measurement units

The units on which measurements are taken (can be the same as or different from experimental units).

Replication

Using multiple experimental units per treatment to reduce variability and increase reliability.

Randomization

Assigning treatments to units by chance to reduce bias.

Blocks and blocking

Grouping similar experimental units together (blocks) and randomizing treatments within those groups to control variability.

Blinding

Keeping subjects and/or researchers unaware of which treatment is given to prevent bias.

Control

A baseline group used for comparison, often receiving no treatment or standard treatment.

Placebo

A fake treatment that looks real but has no active effect.

Quantitative variable

A variable measured numerically.

Qualitative variable

A variable that is categorized.

Continuous variable

A quantitative variable that can take any value within a range (e.g., height, time).

Discrete variable

A quantitative variable that takes countable values (e.g., number of stud

Nominal

A categorical variable with no natural order (e.g., blood type, eye color).

Ordinal

A categorical variable with a meaningful order but unequal spacing (e.g., rankings, satisfaction levels).

Convenience sample

A sample chosen because it is easy to obtain, not necessarily representative.

Population

The entire group of interest in a study.

Sample

A subset of the population used to collect data.

Parameter

A numerical value describing a population (usually unknown).

Statistic

A numerical value calculated from a sample used to estimate a parameter.

Representative

A sample that accurately reflects the population’s characteristics.