# Experimental Psych

## 56 terms · Chapters

### Alternative Hypothesis (H1)

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

### Critical Region

Portion in the tail(s) of the distribution of a test stat extreme enough to satisfy the researcher's criterion.

### Descriptive Statistics

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

### Inferential Statistics

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

### Mean

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. Includes 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 of 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; the critical region of the distribution of the test statistic is measured in just one tail of the distribution

### Range

the difference between the largest and smallest scores in a set of 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

### 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

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 exists 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 STD

### Variance

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

### ANOVA (Analysis of Variance)

Stat procedure used to evaluate differences among three or more treatment means by breaking the variability in the data into components that reflect the influence of error and error plus treatment effects

### A Priori Comparison

Stat test between specific treatment groups that was anticipated, or planned, before the experiment was conducted, also called planned comparison

### Between Groups Variability

Degree to which the scores of different treatment groups differ from one another (how much subjects vary under different levels of the I.V.) a measure of variability produced by treatment effects and error

### Chi Square (x2)

Nonparametric, inferential stat that tests whether the frequencies of responses in our sample represent certain frequencies in the population; used with nominal data

### Confidence Interval

range of values above and below a sample mean that is likely to contain the population mean with the probability level (usually 95% or 99%) that the mean of the population would actually fall somewhere in that range

### Critical Value

Value of the test stat that must be exceeded to reject the null hypothesis at the chosen significance level

### Degrees of Freedom (df)

The number of members of a set of data that can vary or change with out changing the value of a known stat for those data

### Error

The variability within and between treatment groups that is not produced by changes in the I.V.; variability produced by individual differences, experimental error and other extraneous variables

### F Ratio

a test stat used in the analysis of variance; the ratio between the variability observed between treatment groups and the variability observed within treatment groups

### Interaction

the effect of one I.V. changes across the levels of another I.V.

### Main Effect

the action of a single I.V. in an experiment; the change in the d.v. produced by the various levels of a single factor

### Mean Square (MS)

an average squared deviation; a variance estimated used in analysis of variance procedures and found by dividing the sum of squares by the degrees of freedom.

### Mean Square Between Groups (MSb)

Variance across different treatment groups produced by error and treatment effects; found by dividing the sums of squares by the degrees of freedom

### Main Squares Within Groups (MSw)

Variance within a single treatment group; produced by the combination of sources called error

### One Way Between Subjects Analysis of Variance

stat procedure used to evaluate a between subject experiment with three or more levels of single I.V.

### Repeated Measures ANOVA

stat procedure used to evaluate a between subject experiment with three or more levels of a single I.V.

### Post Hoc Test

stat test performed after the overall analysis indicates significant difference; used to pinpoint which differences are significant

### Robust

term describing a stat test that can be used with out increasing the probability of Type 1 and Type 2 errors even though its assumptions are violated

### T test

a stat that relates differences between treatments to the amount of variability expected between any two samples of data from the same population; used to analyze the results of a two group experiment with one I.V. and interval or ratio data

### t test for independent groups

relates difference between treatment means to the amount of variability expected between any two samples of data from the same population; used to analyze the results of a two group experiment with independent groups of subjects

### t test for matched groups

relates differences between treatment means to the amount of variability expected between any two samples of data from the same population; used to analyze two group experiments using matched subjects or within subject designs

### Within Groups Variability

degree to which the scores of subjects in the same treatment group differ from one another; an index of the degree of fluctuation among scores that is attributable to error

### Aggregation

Grouping together and averaging of data gathered in various ways, including aggregation over subjects ; over stimuli and for situations, over trials and for occasions and over measures

### Field Experiment

Experiment conducted outside the lab that is used to increase external validity, verify earlier lab findings, and investigate problems that cannot be studied successfully in the lab

### Manipulation Check

Assessment to determine whether the I.V. was manipulated successfully

### MANOVA

procedure used to study impact of the I.V.s on two or more dependent variables; an extension of analysis of variance

### Naturalistic Observation

Descriptive, non-experimental method of observing behaviors as they occur spontaneously in natural settings

### Reactivity

tendency of subjects to alter their responses or behaviors when they are aware of the presence of an observer