PSYC 274 Midterm 1 Vocab

created by Anthony Andino

What is a population?

The complete group a researcher wants to understand.

What is a sample?

A smaller group selected from the population.

Parameter versus statistic?

A parameter describes a population; a statistic describes a sample.

Descriptive versus inferential statistics?

Descriptive summarizes observed data; inferential uses a sample to draw conclusions about a population.

Independent versus dependent variable?

The IV is manipulated or compared; the DV is measured.

Random sample versus random assignment?

Sampling selects people from a population; assignment places participants into conditions.

What makes groups equivalent?

They do not differ systematically before treatment; remaining differences are random.

What does statistically significant mean?

The result is unlikely to be due only to chance.

What does covary mean?

Two variables change consistently in relation to one another.

What does a correlation coefficient show?

The strength and direction of a relationship.

What is an operational definition?

The exact procedure for manipulating or measuring a variable.

What are empirical data?

Measurements obtained through observation or sensory experience.

Naturalistic observation?

Observe behavior in its normal setting without manipulation.

Archival research?

Use existing records or documents.

Survey research?

Ask people questions through an interview or questionnaire.

True experiment?

Manipulation, control, and random assignment; can support causation.

Quasi-experiment?

Comparison without full random assignment, often using preexisting groups.

Nominal scale?

Categories with no meaningful order.

Ordinal scale?

Ordered categories with unknown or unequal distances.

Interval scale?

Equal intervals but no true zero.

Ratio scale?

Equal intervals plus a true zero.

Discrete versus continuous?

Discrete values are countable; continuous values can fall anywhere within a range.

Real limits for 46 measured to the nearest unit?

45.5 and 46.5.

Qualitative versus quantitative?

Categories or qualities versus numerical counts or measurements.

Relative frequency?

f ÷ total number of scores.

Percentage frequency?

Relative frequency × 100.

Percentile rank?

Percentage of scores at or below a score.

Percentile point?

The raw score located at a stated percentile.

Positive skew?

Long tail to the right; mean often above median.

Negative skew?

Long tail to the left; mean often below median.

Bimodal?

Two values share the highest frequency.

When is the mean best?

Fairly symmetric interval or ratio data without major outliers.

When is the median best?

Skewed data, ordinal data, or data with outliers.

When is the mode best?

Nominal data or when the most common category matters.

Range?

Highest score minus lowest score.

Why can a graph mislead?

Its scale may be missing, uneven, truncated, or poorly labeled.

Sum of squares?

Σ(X − mean)².

Variance?

Average squared distance from the mean.

Standard deviation?

Square root of variance; typical distance from the mean.

Why use n − 1?

It corrects the sample tendency to underestimate population variance.

What does SD = 0 mean?

All scores are identical.

Four traits of a normal distribution