cdis 5400 dr brenda louw 2010. terminology populations and samples ◦ sample characteristics ◦...
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Terminology
Populations and Samples◦ Sample characteristics◦ Selection criteria◦ Sampling methods◦ Sample size ◦ Power analysis
Research ethics
Overview
Subjects:◦ Traditional quantitative scientific research
Participants◦ Qualitative research ◦ APA 2001 recommendation
Complicating factors◦ Research design terminology e.g. Single subject
design, within-subject design◦ Individuals who participate, but cannot give
Informed consent`
Terminology
Currently :◦ Subjects in quantitative research ◦ Participants in qualitative research ◦ Respondents in survey studies(questionnaires)◦ Examinees in test-developing research◦ Also observers, listeners, judges, raters depending
on research task, design
Gender vs biological sex◦ APA :
gender refers to role, cultural biological sex: female or male
Terminology
Other:◦ Animals◦ Specimens and tissue samples◦ Descriptions required◦ Research ethics and IRB
Conclusion:◦ Irrespective of terminology : describe individuals
clearly, concisely
Terminology
1st step in research design and planning - identify population of interest/ target population
Use of entire population - census Extract sample of target population
◦ make inferences about the population based on data from a sample
◦ Indirect conclusions
Populations and Samples
Sample needs to represent population Representative sample
◦ good match of characteristics of the population◦ Include individuals from each constituency of the target
population –including women and children Sample depends on purpose and methodology Bias in selecting sample
◦ Unbiased sample-all members of population have equal chance of being included
◦ Sources of bias: failing to identify all members of a population using sample of convenience volunteerism
Sample characteristics
De Kroon et al.,2002 LSHSS Investigated language impaired children’s
social pretend play and conversational behaviors
Selected 7 boys as participants-3 LI and 4 normal language development
Is the sample representative of the population of children with LI ?
e.g. Meline 2010
Erler & Garstecki @002) AJA Do women vary by age in the degree of
stigma they attach to hearing loss and HA use?
191 women as participants Do the participants match the stated
purpose of the research?
e.g. Meline 2010.
Establishing selection criteria critical aspect in planning research
Selection criteria important to validity and generalization, transferability of results◦ e.g results due to IV or unreported subject
variables Criteria crucial in between-subject designs-
comparison of 2 groups
Selection criteria
Need to describe, define and defend criteria
Samples not all homogenous and lack of detailed descriptions implies that they are
Sufficient detail required to:◦ replicate the study◦ generalize conclusions to real-life situations
Critical reviews◦ Schmitt & Meline(1990) examined 92 research reports with LI
children-only 30% included information about individual participants
Selection criteria continued
Reilly and Moore,2009 Infant respiratory movements during vocalizations (JSHR, 52,223-239)
40 infants: born within 2 weeks of their due date, weighed at least 6 lbs at bith, had negative medical histories for respiratory, cardiovascular and neurological disease, monolingual English homes.
Exclusion criteria: ear infections in week prior to testing, family history hereditary HL, family members with speech, language disorders
e.g.
Simple random sampling Stratified random sampling Cluster sampling Purposive sampling
Sampling methods
◦ Enhances external validity◦ Improves generalization to the target population◦ Every member of the population has an equal
chance of being selected for the study◦ Use random numbers e.g. assign all participants a
number, consult table of random numbers or random number function in spreadsheets
◦ Time consuming method◦ Seldomly used
Simple random sampling
Divide accessible population into subgroups/strata
Then draw subjects randomly E.g. stratify according to age, sex, socio-
economic level, parent education levels etc.,
and then determine groups
Stratified random sampling
Used for large numbers of participants Start with obtaining random sample of
predetermined groups e.g. classroom , community, clinic
Multistage sampling-e.g. choose school district randomly, then select one school from district randomly ,then select one classroom ,then select the children
Cluster sampling
Research question requires input from special persons, groups
Purposeful effort required to identify them Recruit subjects
Purposive sampling
Broad range of sample size due to diversity of research in Communication Disorders
The purpose of the study, nature of the research design and variability of the data determines the adequacy of the sample size
E.g. ◦ within –subject designs-many repeated
observations and data points-require small sample◦ between subject designs require larger sample size◦ survey research requires large numbers;◦ single subject designs-small numbers
Sample size
Recruiting large samples problematic in communication disorder research
No absolute numbers but variable numbers determined by how large the population is ,how variable the population is for the characteristics under study etc.
Sample size
Sample size contributes to power of the research design
Power is the ability of a research study to detect significant treatment effects when they are present (Meline, 2010).
2 general uses of power analysis◦ a priori –to determine subject sample size to reach a
given alpha level◦ post hoc- to further evaluate research that has
been completed to determine if failure to reject a null hypothesis was related to an insufficiently large sample size
Power of research design
When all else is equal, research designs with more participants will have more power to identify treatment effects
80% power recommended for detecting moderate-sized effects
Computer software to perform power or sample size calculations e.g. STAT POWER, NQUERY
Continued…
Schiavetti et al.,2011 Chapter 5, p228 8 evaluation items in the methods section
Evaluation of subjects/participants when reviewing research
Study the methods section of a research article Identify the
◦ size of the sample◦ the method of selection◦ Selection criteria
What is the purpose for including each criterion Is sample size adequate for the purpose of the
study? Is an adequate description provided of the
participants Is there evidence of adequate protection of
Ss/participants
Excercise