Week 5 Flashcards by macy walker

What is experimental research?

Designed to control for confounding variables
based on logic, changes are systematically introduced, “cause & effect”

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Extraneous variables

any factor NOT related to the purpose of the study
may affect dependent variables

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In experimental research, the control group may receive what?

standard treatment, no treatment/”wait and see”, placebo treatment

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What is the gold standard of experimental research?

RCT

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three essential components of true experimental designs

independent variable “manipulated” by the experimenter
Include a control or comparison group
participants are randomly assigned to groups

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What is random assignment?

** not the same as random sampling **
each participant has EQUAL chance of being assigned to any group
helps control for extraneous variables or prognostic indicators
should result in homogeneous groups at baseline (not IV)

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Random Assignment Strategies

Simple random assignment
Block random assignment
Stratified random assignment
Cluster random assignment

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What is simple random assignment

coin flip
every person has an equal chance to be in either group
can have UNEVEN groups

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what is block random assignment

envelopes
divided equally into “blocks”
assures groups will be evenly distributed by group or treatment sequence

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what is stratified random assignment

used when certain characteristics (attributes) may be confounding

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what is cluster random assignment

ex: 3 different hospitals
clusters are formed, and each cluster is randomly assigned a treatment
-all members of a cluster get the same treatment

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Concealed Allocation

the researchers do NOT know group assignment

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types of Experimental Design Validity

statistical conclusion validity
internal validity
construct validity
external validity

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statistical conclusion validity

“is there a relationship between the independent and dependent variables?”

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Internal Validity

“is there evidence of a causal relationship between independent and dependent variables?”

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Construct Validity

“to what constructs can results be generalized?”

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external validity

can the results be generalized to other persons, settings, or times?

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assumption of causality requires three components:

Temporal precedence
Covariation of cause and effect
no plausible alternative explanation

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temporal precedence definition

cause precedes effect

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covariation of cause and effect definition

outcome ONLY occurs in the presence of the intervention

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No plausible alternative explanation definition

consider confounding variables

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Internal Validity Internal Threats

History, Maturation, Attrition, Testing, Instrumentation, Regression to the mean, Selection, and Social Interaction

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Internal Threat: History

an unrelated event influences outcomes - did something else happen between measurements?
ex: caffeine

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Internal Threat: Maturation

Passage of time affects DV

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Internal Threat: Attrition

"experimental mortality" -patients drop out diet to restrictive? diet not working?

Internal Threat: Testing

Collection data changes the response

Internal Threat: Instrumentation

a measuring instrument (or measurer) changes over times

Internal Threat: Regression to the mean

extreme scores become less extreme over time

Internal Threat: Selection

Problematic when participants self-select groups addressed with random assignment

Internal Threat: Social Interaction

- diffusion/imitation - compensatory equalization - compensatory rivalry - demoralization

Internal validity social threats

Diffusion/imitation, compensatory equalization, compensatory rivalry, demoralization

Social threats: Diffusion/imitation

participants in control group changed behavior to match experimental group

Social threats: Compensatory equalization

Researchers treat participants in control group differently to make up the difference -researcher feels bad for a group

Social threats: compensatory rivalry

participants in control group look at a LOT of puppy photos to increase happiness

Social threats: demoralization

participants in the control group "give up"

Ruling Out threats to internal validity

random assignment and blinding

types of blinding

single = patient doesn't know double = patient + PT OR patient + assessor triple = extremely rare

Threats to Construct validity

operational definitions, comprehensive measurements, time frame, multiple treatment interactions

Threats to external validity

- influence of selection - influence of settings - influence of history

influence of selection definition

age, gender, diagnosis

Influence of settings definition

RCT vs Pragmatic clinical trials

Influence of history

older studies still have value!

with Noncompliance participants may:

- refuse the assigned treatment after allocation - cross over to another group - be compliant with assigned treatments - withdraw from the study

Missing Data

- needs to be accounted for throughout trial - concerning if > 20% - a problem if related to treatment - drop-outs? switch-overs?

Per Protocol Analysis

analyze only those who completed study

Intention-to-Treat (ITT) Analysis

-analyze in the group that they were assigned to -imputation: estimating missing data values

Researchers can minimize bias using

randomization, concealed allocation, blinding, and ITT

Internal threats are

INSIDE the study (methodology)

External threats are

OUTSIDE the study (generalizing)

True Experimental design is

1. IV "manipulated" by researcher 2. at least two comparison groups 3. subjects randomly assigned

Quasi-experimental designs

- may lack randomization - may lack comparison group - may lack both

types of experimental designs

- between-subjects design - within-subjects - factorial

Between-subjects design

assigned to independent groups

Within-subjects design

participants act as their own controls

Factorial design

how we describe designs that have 2+ IV - two-way design, 3x3 factorial design

One-way Designs

only 1 IV AKA single-factor designs Pretest-posttest control group design - used to compare 2 or more groups formed by random assignment

Pretest-Posttest control group design

- both groups are measured before and after treatment - cause and effect - internal validity is strong

Posttest-only Control Group Design

- similar to pretest-posttest control group, but no pretest is administered to either group - used when pretest is impractical, contraindicated, or potentially reactive - internal validity is strong

what should we assume about the posttest-only control group design

assume groups are equivalent due to random assignment best with large group of subjects

Factorial designs for independent groups

Two-way factorial design Randomized block design

Two-way factorial design

- incorporates **two or more** independent variables - randomly assigned to various combinations of the levels of the variables

Randomized block design

- 1 IV is not randomized - attribute variable - blocked

Benefits of factorial designs for ind groups

gives you information beyond what a single-factor (one-way) design would

Challenges of factorial designs for ind groups

- Larger sample - results of analysis can be difficult to interpret

Naming Factorial Designs definition

- described according to the number of IVs - number of levels within each factor

Designs for Repeated Measures

same people in each level of the IV - within-subject design

One-way (aka single-factor) repeated measures design

- subjects are exposed to all levels of the IV - there is no control group

Effects of Repeated Measures

- practice effects - carryover effects - order effects

practice effects definition

the more you do something, the more efficient you become

carryover effects definition

the effects of the first rx still present when second rx is introduced

Order effects definition

use of Latin Square as a possible solution of order effects

Crossover designs

- participants are randomized to a treatment sequence - used to control for order effects - considerations for washout period

Two-way (multi-factor) repeated measures design

all IVs are "repeated" or "within-subject"

Experimental designs can be _____

between-subject, or within-subject, or mixed

a one-way pretest-posttest control group design is the _______

most basic structure of a RCT

A week before the end of the study, all employees are told that there will be layoffs. The participants are stressed on the date of the post-test, and performance may suffer. What type of internal threat?

History

What type of internal threat? Most participants are new to the job at the time of the pre-test. A month later, their productivity has improved as a result of time spent working in the position.

maturation

What type of internal threat? In the pre-test, productivity was measured for 15 minutes, while the post-test was over 30 minutes long.

Instrumentation

What type of internal threat? Participants showed higher productivity at the end of the study because the same test was administered. Due to familiarity, or awareness of the study’s purpose, many participants achieved high results.

Testing

What type of internal threat? Low-scorers were placed in Group A, while high-scorers were placed in Group B. Because there are already systematic differences between the groups at the baseline, any improvements in group scores may be due to reasons other than the treatment.

Selection bias

What type of internal threat? Because participants are placed into groups based on their initial scores, it’s hard to say whether the outcomes would be due to the treatment or statistical norms.

Regression to the mean

What type of internal threat? Groups B and C may resent Group A because of the access to a phone during class. As such, they could be demoralized and perform poorly.

Social interaction

What type of internal threat? 20% of participants provided unusable data. Almost all of them were from Group C. As a result, it’s hard to compare the two treatment groups to a control group.

Attrition bias

Week 5 Flashcards

(83 cards)