Chapter 11 - Confounding and Obscuring Variables

Question 1

For single group pretest-posttest designs, there are six possible thereat that can affect internal validity, what are they?

Answer 1

Maturation

History of effects

Regression to the mean

Attrition

Testing threats (test repetition effect)

Instrumental test

Question 2

Maturation

Answer 2

Participants automatically become better at tasks over time

Question 3

History of effects

Answer 3

Between pre- and post-test something happened to most participants, making it unclear whether the change was due to the manipulation or something else

It is wise to sue a comparison group for this as well

Question 4

Regression to the mean

Answer 4

An experimental group changes over time because the most extreme cases are systematically removed during the study, so that they are not included in the follow up measurement

Question 5

Why is attrition an issue when it happens systematically?

Answer 5

When only a certain type of participant drops out

Question 6

Testing threats (test repetition effect)

Answer 6

Is a type of sequence effect where an experimental group changes over time, because related testing affects participants

After a number of tests, they may be tired or bored, so they will perform less well

Question 7

When is it best to use a posttest?

Answer 7

Using a posttest only with a control group or to use different variants of the test otherwise

Question 8

Instrumentation test

Answer 8

When a measurement instrument changes over time

Criteria have changed at posttest (like observers)

Different tests (such as observers) used you don’t know where the difference comes from

Question 9

What is the difference between testing and instrumentation?

Answer 9

With testing, the participants are changed and with instrumentation the measuring instrument

Question 10

What are the threats to internal validity for all types of experiments?

Answer 10

Observer bias

Placebo effect

Question 11

Observer bias

Answer 11

Expectations colour the observation

Question 12

Demand characteristics (also observer effect)

Answer 12

Participants try to guess what the researcher wants to know and act/respond accordingly

Question 13

How to reduce the problem of demand characteristics?

Answer 13

Double blind study

Masked design

Question 14

What is a masked design?

Answer 14

Researchers do not know which group the participants are in

Question 15

Placebo effect

Answer 15

Participants in the experimental group improve because they believe in the effect of the therapy or medicine they received, even if ti is a placebo

Question 16

What are the causes of a null effect/null result?

Answer 16

Not a large enough between groups difference due to weak manipulations, a not sensitive enough measurement instrument or ceiling and floor effects

Question 17

Ceiling and floor effects

Answer 17

With a ceiling effect, all the scores clustered together on the high side and with a floor effect, that cluster is on the low side

Question 18

What can the cause be of a ceiling and floor effect?

Answer 18

Can be caused by a badly manipulated independent or dependent variable

Question 19

Within group variability (noise)

Answer 19

Can overshadow the effects

This can include measurement error, individuals differences, situational noise, and power

Question 20

Individual differences

Answer 20

Participants differ in certain aspects such as motivation and ability

For example, reading a text

Question 21

Situational noise

Answer 21

A noisy location can cause participants to become distracted