Single-Variable, Independent-Groups Designs + The normal distribution + t-test for unpaired observations +

Question 1

What is the ex post facto design?

Answer 1

the researcher observes currently present behavior to then relate it to past experiences. There is no control for confounders and no causality can be determined , meaning rival hypotheses can not be rejected.

Question 2

one group, single post-test design

Answer 2

there is a manipulation, but since there is no pre-measurement, there are still confounding factors and no causality can be established.
There is no control over possible placebo-effects, maturation, history, or regression to the mean.

Question 3

One group, pre- and post-test design:

Answer 3

Nonexperimental
design in which participants are measured on a dependent
variable both before and after the manipulation., it is a time-series design.

Question 4

Pre- and post-test, natural control group design

Answer 4

Design
in which preexisting groups are measured before and
after the manipulation of an independent variable.

Question 5

How are experimental designs distinguished from non-experimental design?

Answer 5

Two elements: Control Groups or control conditions and random assignment.

Question 6

Randomized, single post-test, control group design:

Answer 6

Experimental
design in which participants are randomly
assigned to two groups, and each group is tested on
the dependent variable after the independent variable
manipulation

Question 7

Randomized, pre- and post-test, control group design:

Answer 7

Experimental design in which participants are randomly
assigned to two groups, and each participant is
tested on the dependent variable both before and after
the manipulation.

Recall that the pretest-posttest, natural control-group design discussed earlier is not
an experiment because it does not include random assignment to groups.

Question 8

What can be some disadvantage of the pre-measurement

How can we try to control it?

Answer 8

pretest-manipulation interaction effect

Solomon’s four-group design
(Solomon, 1949). It is a powerful design that combines the randomized, pretest-posttest,
control-group design and the posttest-only, control-group design. However, because it requires the
resources of two experiments, it is not recommended for routine use.

Question 9

What is unbiased assignment and how do we achieve it?

Answer 9

Assigning participants to groups
or conditions in such a way that the groups are statistically
equivalent at the start of the study. The most
common unbiased assignment method is random
assignment.

Question 10

Multilevel, completely randomized between subject design:

Answer 10

A design with more than two groups, in
which each participant is randomly assigned to one
group. If there is a pre-test depends on the nature of the study.

Question 11

What is a between-subjects design?

Answer 11

Different parrticipants in each condition

Question 12

What are within-sunject designs or matched-subject designs?

Answer 12

the same participants or matched participants in each condition

Question 13

What is ment by single-variable designs:

Answer 13

Designs that include just one independent

variable.

Question 14

What would be the counterpart to single-variable designs?

Answer 14

factorial design

Question 15

What characteristics has to have a statistics?

Answer 15

1. The value can be calculated from the data

2. The probability distribution under H0is known

Question 16

Name characteristics for unpaired t-test!

Answer 16

assume that analysed data is from a normal distribution.
there is also the assumption that the standard deviation (SD)s is approximately the same in both groups.
data of different participants in different conditions
(groups)
e.g. in an between subject design

Question 17

Characteristics of a paired t-test!

Answer 17

same as unpaired t-test but (!) : data of the same participants in different conditions

Question 18

How can we measure an unpaired t-test, if we have the data (means andstandard deviation) of two groups?

Answer 18

t=[(m1-m2)/(s1+s2)]x(-^n1+n29)

m1 & m2 are group means
s1 and s2 are standard deviations

Question 19

When is t more extreme and what does it mean?

Answer 19

When it deviates a lot from 0.

1. if the effect (m1-m2) is more extreme (“signal”)
2. the spread between groups (s1+s2) is smaller (“noise”)
3. the number of subjects per group is larger

Question 20

What determines t?

Answer 20

the trinity of lecture 5 and 6… :D

Question 21

What does t has to be to have more evidence against the null hypothesis?

Answer 21

more extreme (high or low)

Question 22

Are the probability distributions of the t-test und H0 and that of the standard normal distribution (z) the same)

Answer 22

Only if n1 and n2 are extremely large

asthey are smaller the difference between t and z is bigger

Question 23

two more things that one should know about t distributions!

Answer 23

1. they are a family of distributions
2. the exact shape of t-distribution is determined by the “degree of freedom” The degrees of freedom refers to the number of independent observations in a set of data.

Question 24

At which t-value is the two tailed 5%p-value reached in the (1) t-distribution and in the (2) (z)distribution

Answer 24

(z) +- 1,96
(t) +- 2,57

now that matters!

Question 25

Can you please explain the difference between descriptive and inferential statistics?

Answer 25

Descriptive statistics: what are the main characteristics of the data? m1, m2, s1, s2.

Inferential statistics: what conclusions do the data allow about the population? t(18) = -3.24, p < 0.05.

Question 26

What is the advantage of random assignment?

Answer 26

Effective control for: history, maturation, regression to the mean, testing, and instrumentation.