Chapter 7 the basics of experimentation

Independent variable (IV)

is the dimension that the experimenter intentionally manipulates; it is the antecedent the experimenter chooses to vary.

Independent variable (IV)

This variable is __ in the sense that its values are created by the experimenter and are not affected by anything else that happens in the experiment.

Independent variable (IV)

also referred as treatments, manipulations, interventions, conditions

potential IVs

the physical environment that can be brought under the experimenter's direct control.

potential IVs

Lighting (bright or dim) and noise levels (loud or soft)

potential IVs

Aspects of a given task, such as diffi-culty (easy, hard) and meaningfulness

potential IVs

failing-psychological states

Independent variable (IV)

at least two different treatment conditions are required

Independent variable (IV)

must be given at least two possible values in every experiment.

researcher

decides which values of the IV to use.

ex post facto and other quasi-experimental studies

, researchers often behave as if they were doing true experiments; they have treatments and mea-sured observations

true experiment

, we test the effects of a manipulated independent variable not the effects of different kinds of subjects.

Dependent variable (DV)

is the particular behavior we expect to change because of our experimental treatment; it is the outcome we are trying to explain.

Dependent variable (DV)

also referred to as measures, effects, outcomes,results

Dependent measures

Because we manipulate the IV and measure its effects on the DV, dependent variables are sometimes called .

Dependent measures

dependent in the sense that its values are assumed to depend on the values of the independent variable

Operational definition

specifies the exact meaning of a variable within an experiment

Operational definition

It defines a variable in terms of observable operations, procedures, and measurements.

Operational definition

include in written reports of experiments so that other researchers will understand exactly what was done and will be able to replicate it.

Experimental operational

definitions explain the precise meaning of the independent variables

Experimental operational

these definitions describe exactly what was done to create the various treatment conditions of the experiment.

Measured operational definitions

describe exactly what procedures we follow to assess the impact of different treatment conditions

Hypothetical constructs

unseen processes postulated to explain behavior but cannot be observed directly.

Nonconstruct

variable directly observed

Internal validity

is the degree to which a researcher is able to state a causal relationship between antecedent conditions and the subsequent observed behavior.

Internal validity

conclusions, credible and trustworthy without high internal validity; experiment cant demonstrate a causal \ link between 2 variables

extraneous variables

not the focus of the experiment but can influence the findings.

extraneous variables

potential to influence DV

extraneous variables

They can include differences among subjects, equipment failures, inconsistent instructions-in short, any-thing that varies within the experiment.

1. your treatment and response variables change together 2. treatment precedes 3. no confounding

3 necessary conditions

construct founding

influences both the supposed cause and supposed effect

construct founding

also called confounders or confounding factors, closely related to study's IV and DV

History

events occur between the first and second instruments

Maturation

, refers to any internal (physical or psy-chological) changes in subjects that might have affected scores on the depen-dent measure (

Testing

effects of taking a test on the outcomes of taking a second test

Instrumentation

changes in the instrument, observersm or scorers which may produce changes in outcomes

Statistical Regression

called regression toward the mean

Statistical Regression

selection of subjects on the basis of extreme scores of chaaracteristics

Selection

selection of comparison groups

Randominization

random assignment of group memberships is a counter attack against this threat

Subject morality

loss of subjects

Selection interaction

A selection threat can combine with another threat to form a __

Method

section of the research report is the place to describe what you did in your experiment

Method section

is divided into labeled subsections such as Participants, Materials, and Procedure,

Participants or Subjects

to describe your subjects

Participants or Subjects

who they are, how many, how they were selected

Materials

for written items and Stimuli or Interventions

Materials

describe any special or unusual equipment or software used in the study

Procedure

detailed procedure

Procedure

explain what you had participants do

Procedure

Listing them in chronological order is often the simplest way to pres-ent your procedures.