EXPE reviewer key terms Ch 13-15 + 3

Alternative hypothesis (H₁)

A statement that the data came from different population; the research hypothesis, which cannot be tested directly.

Critical region

Portion in the tail(s) of the distribution of a test statistic extreme enough to satisfy the researcher’s criterion for rejecting the null hypothesis—for instance, the most extreme 5% of a distribution where p<.05 is the chosen significance level.

Descriptive statistics

The standard procedures used to summarize and describe data quickly and clearly; summary statistics reported for an experiment, including mean, range, and standard deviation.

Directional hypothesis

A statement that predicts the exact pattern of results that will be observed, such as which treatment group will perform best.

Experimental error

Variation in subjects’ scores produced by uncontrolled extraneous variables in the experimental procedure, experimenter bias, or other influences on subjects not related to effects of the independent variable.I

Inferential statistics

Statistics that can be used as indicators of what is going on in a population; also called test statistics

Mean

An arithmetical average computed by dividing the sum of a group of scores by the total number of scores; a measure of central tendency.

Measures of central tendency

Summary statistics that describe what is typical of a distribution of scores; include mean, median, and mode.

Median

The score that divides a distribution in half, so that half the scores in the distribution fall above the median, half below; a measure of central tendency

Mode

The most frequently occurring score in a distribution; a measure of central tendency.

Nondirectional hypothesis

A statement that predicts a difference between treatment groups without predicting the exact pattern results.

Normal curve

The distribution of data in a symmetrical, bell-shaped curve.

Null hypothesis (H₀)

A statement that the performance of treatment groups is so similar that the groups must belong to the same population; a way of saying that the experimental manipulation had no important effect.

One-tailed test

A statistical procedure used when a directional prediction has been made; statistics is measured in just one tail of the distribution.

Range

The difference between the largest and smallest scores in a set data; a rough indication of the amount of variability in the data.

Raw data

Data recorded as an experiment is run; the responses of individual subjects

Significance level

The statistical criterion for deciding whether to reject the null hypothesis or not, typically p<.05.

Standard deviation

The square root of the variance; measures the average deviation of scores about the mean, thus reflecting the amount of variability in the data.

Statistical inference

A statement made about a population and all its samples based on the samples observed.

Statistical significance

Meeting the set criterion for significance; the data do not support the null hypothesis, confirming a difference between the groups that occurred as a result of the experiment.

Statistics

Quantitative measurements of samples; quantitative data

Summary data

Descriptive statistics computed from the raw data of an experiment, including the measures of central tendency and variability.

Test statistics

Statistics that can be used as indicators of what is going on in a population and can be used to evaluate results; also called inferential statistics

Two-tailed test

A statistical procedure used when a nondirectional prediction has been made; the critical region of the distribution of the test statistic is divided over both tails of the distribution.

Type 1 error

An error made by rejecting the null hypothesis even though it is really true; stating that an effect exist when it really does not.

Type 2 error

An error made by failing to reject the null hypothesis even though it is really false; failing to detect a treatment effect.

Variability

Fluctuation in data; can be defined numerically as the range, variance, or standard deviation.

Variance

The average squared deviation of scores from their mean; a more precise measure of variability than the range.