Experimental Design #1

Observational study

observe outcomes without imposing any
treatment

Experiment

actively impose some treatment in order to observe the
response

Survey

simply asking respondents for data, no observation or treatments

Experimental unit

the single individual (person, animal, plant,
etc.) to which the different treatments are assigned

Factor

is the explanatory variable – it’s what we test

Level

a specific value for the factor

Response variable

what you measure

Treatment

a specific experimental condition applied to the units

Control group

a group that is used to compare the factor against;
can be a placebo or the “old” or current item

Placebo

a “dummy” treatment that can have no physical effect

blinding

method used so that units do not know which
treatment they are getting

double blind

neither the units nor the evaluator know which
treatment a subject received

Confounding variable

A variable whose effect on the response cannot be separated or distinguished from the effects of the factor on the response.

- a variable that is related to both group
membership and the response variable of
interest in a research study

Control

the effects of extraneous
variables on the response

Randomization

the use of chance to assign subjects to treatments

Replication

of the experiment on many subjects to quantify the natural variation in the experiment

Treatments-

the experiment must have
two or more treatments

The ONLY way to show cause
& effect is with

a well-designed,
well-controlled experiment!!!