Group Design Flashcards
Describe Experimental Designs: (5)
- Experimental Research – ACTIVE CONTROL of independent variable by the experimenter
-Can be group or single-subject - Individual or group design is based on how data are analyzed, not on how many participants are involved or how they are treated/tested
- Group: Individuals’ data are combined for analysis
Single-subject: Each individual’s data are analyzed separately - Some group studies may provide individual data as a follow-up to group results
Experimental Group Designs is highly _________________ and has the highest ___________ _______________ if well designed.
Highly controlled: highest internal validity if well designed
What makes the Experimental Group design Highly controlled and highest internal validity? (3)
- Manipulation of independent variable
- Appropriate control(comparison) group/condition
- Random assignment to group/condition
What makes Quasi-experimental design weaker than Experimental design?
- Sometimes impossible to meet stringent experimental requirements
- Weaker design than true experimental
- Often treated like experimental
- Not all questions allow experimental (e.g., comparing TD and TBI – no random assignment)
What are two types of assignments in Quasi-Experiments? (Consequences and Examples)
A) no control group/condition
Consequence: no comparison group
e.g., simple pretest-treat-posttest; all participants experience IV
B) no random assignment
Consequence: possibly non-equivalent groups
Examples
Naturally occurring
E.g., treatment 1 in school ‘A’, treatment 2 in school ‘B’
People on waiting list
History control group – file review of patients before offered experimental treatment
Those who declined treatment as control group
What is the internal Validity in Quasi-Experimental designs?
Internal validity & confidence in results is reduced
Less faith in attributing the cause of the change the treatment
How can we increase validity in quasi-experimental studies? (3)
- Describe subjects carefully
- Test for equivalence (but can’t test for everything)
- Match groups on critical parameters
-Choose control participants so that they match experimental participants on parameters, e.g., MA, SES
What is Between Subjects design?
- Separate groups of independent participants who are sampled only once
- If multiple measures given, all comparisons between groups
Compare Grp 1 vs Grp 2 on measure 1
Compare Grp 1 vs Grp 2 on measure 2 - Less common in treatment studies
- When use ‘gain scores’
What is the difference between N and n in group designs?
‘N’ – total number of participants in study
‘n’ – number of participants in each group
What is the difference between N and n in group designs?
‘N’ – total number of participants in study
‘n’ – number of participants in each group
What are the assumptions in Experimental Group designs?
- Variability in data is intrinsic to participants
- Large groups and random assignment balances this noise/error in the study between the control & experimental group
- When balanced, assume a difference between groups is the result of the independent variable
- Randomization gives you balanced groups
- Inferential statistical analysis on grouped data allows the determination of ‘significant’ difference
- Can generalize to population (assumes sample represents population)
What is Within Subject/Related Samples/ Repeated Measures?
- Participants sampled on same measure more than once.
- One Grp compared at Time 1 and Time 2
- Single-group pretest-posttest design & Time series design
OR
- Participants are related (e.g., siblings, classmates)
-1st born are compared to 2nd born
OR - Participants sampled on multiple conditions/measures and comparisons made within the group
-One Grp condition/measure1 compared to condition/measure 2
N = number of participants
What is a concern in Within Subject/Related Samples/ Repeated Measures?
Order or carry-over effects,
e.g., Participants perform a task better in later conditions because they have had a chance to practice it.
What is the most common group design in Experimental designs?
Mixed (Between +Within Subjects)
What are the characteristics of Mixed group design?
- Contains both between and within-subject variables.
- Standard treatment study
Treatment group vs control group (between)
Tested Pretest & Posttest therapy (within)
Here is an example of Comparing hearing aid 1 vs 2 (Between Within and Mixed)
Between
N = 20 in 2 groups; n = 10
Grp 1 = HA-1; Grp 2 HA-2
IV: type of aid; DV: speech perception score
Within
N = 20; n = 20
Each participant wears HA-1 1 wk, HA-2 1 wk
IV: type of aid; DV: speech perception score
To control order effect, better if ½ do HA-1 1st & ½ do HA-2 1st
Mixed
10 mild HL, 10 moderate HL, 10 severe HL – N = 30; n = 10
Each participant wears HA-1 1 wk, HA-2 1 wk
IV between: hearing level; IV within: type of aid; DV: speech perception score
To control order effect, better if ½ do HA-1 1st & ½ do HA-2 1st in each group
Here is an example of Comparing hearing aid 1 vs 2 (Between Within and Mixed)
Between
N = 20 in 2 groups; n = 10
Grp 1 = HA-1; Grp 2 HA-2
IV: type of aid; DV: speech perception score
Within
N = 20; n = 20
Each participant wears HA-1 1 wk, HA-2 1 wk
IV: type of aid; DV: speech perception score
To control order effect, better if ½ do HA-1 1st & ½ do HA-2 1st
Mixed
10 mild HL, 10 moderate HL, 10 severe HL – N = 30; n = 10
Each participant wears HA-1 1 wk, HA-2 1 wk
IV between: hearing level; IV within: type of aid; DV: speech perception score
To control order effect, better if ½ do HA-1 1st & ½ do HA-2 1st in each group
What is the difference between longitudinal and cross-sectional?
Longitudinal: observational research technique involves studying the same group of individuals over an extended period. Variables that are not related to various background variables
Cross- Sectional: Type of research design in which you collect data from many different individuals at a single point in time. In cross-sectional research, you observe variables without influencing them
What is the difference between a Prospective and Retrospective study design?
Prospective: individuals are followed over time and data about them is collected as their characteristics or circumstances change
Retrospective: Individuals are sampled and information is collected about their past
Explain Degrees of Freedom:
When computing any statistical test, Degrees of Freedom (df) need to be determine, the size and number of groups being compared
The number of independent pieces of information used to calculate a statistic.
the extent to which components in a design are free to vary
What are parametric statistics? (5)
- Normal distribution
- Homogeneity of variance (groups have about the same amount of variance)
- Interval or ratio data
- Large ‘N’
- Equal ‘n’
If you violate too many parametric statistics you should use:
Nonparametric
With which type of data do you often see parametric analyses?
Often see parametric analyses used with ordinal data – e.g., from rating scale
Why are df necessary?
Necessary to determine critical value for test statistic to reach alpha level (i.e., p value associated with statistic).
What is df influenced by?
Influenced by number of participants, their scores and the number of independent (i.e. grouping) variables
As df __________________ (larger N, fewer groups give larger df) critical value of statistic (t, F etc.) _____________so easier to reach significance
As df increases (larger N, fewer groups give larger df) critical value of statistic (t, F etc.) decreases so easier to reach significance
What is the meaning of univariate?
Only 1 dependent variable
What is Multivariate?
More than 1 dependent variable
e.g., receptive & expressive language tests
e.g., assess HA via speech discrimination & client satisfaction