WEEK 2: SAMPLING DATA COLLECTION Flashcards
Probability Sampling
Involves using selection techniques where in the probability of selecting each sampling unit is known
Stratified Sampling
RANDOM
- 3 from each stratum are randomly selected
Random samples from distinct groups (i.e sex: male, female. Geography: urban, rural)
Simple Random Sampling
most challenging and expensive
- each person has an equal chance of being selected
Cluster Sampling
- Convenient and less expensive
- Lack random selection
- Natural clusters (schools, neighborhoods) rather than individuals units
- Observations are made on ALL units within a cluster
Multistage Sampling
- Cluster is involved in this sampling
- Primary sampling units are selected
I.e Western students
Secondary units selected within primary units
I.e Students in Health Sci program
Can have more levels
Teriery units - i.e students at western in the health sci program, in 2nd year
Every type of person involved in this sample
Convenience Sampling
selection from a non-probability based source population due to ease of access to those individuals, schools, workplaces, organizations or communities
Purposive Sampling
recruitment of the participants for a qualitative study based on the special insights they can provide
Key Informants
individuals selected to participate in a qualitative study because they have expertise relevant to the study question
Berksons Bias
can occur when cases and controls for a study are recruited from hospitals and therefore are more likely than the general population to have comorbid conditions
Healthy worker bias
can occur when participants are recruited from occupational populations and therefore are systematically heather than the general population
Exclusion bias
occurs when different eligibility criteria are applied to cases and controls, such as when controls with health conditions related to an exposure are excluded but cases with those comorbidities are not excluded
Type 1 Error (A)
occurs when a study population yields a statistically significant test result even thought a significant different or association does not actually exist in the source population
- Rejected null hypothesis even tho it was true
Type 2 Error (B)
occurs when a statistical test of data from research finds no significant result even thought a significant difference or association actually exists in the source population
- Null hypothesis is false and failed to reject it
Interview
is: the process of verbally asking a participant questions and recording that persons responses
Self Administered Survey
questionnaire form that participants complete by themselves, using either a paper and pencil version or online
Semi Structured Interview
the interview starts with a list of open ended questions that will be asked of each participant, but these questions or lists of topics are merely starting points for electing responses from participants
Probing
is an interview technique that prompts an interviewee to provide a more complete or specific response
Interviewer Bias
occurs when interviewers systematically questions cases and controls or exposed and unexposed members of a study population differently, such as probing only individuals they believe to have the disease or exposure of interest for more information
Uniformity
easiest to accomplish when all interviewers are provided with the tools they need to follow a standardized set of procedures
Close ended questions
allow a limited number of possible responses
-date and time questions
-numeric questions
-categorical
o ranked (ordinal) categorical answers have an inherent order
o unordered (nominal) categorical answers do not have any built in order
- paired comparisons
Pros and Cons of a self administered survey
pros: cost and time efficient, possibility of approaching a large number of partipants, honest answer to sensitive questions
cons: low literacy populations, limited internet
- Order of Questions
- better to start with easy or at least general questions before moving to more difficult or sensitive questions
- it is often best to group similar questions with similar response types, so that they are asked consecutively
Pilot Testing
A small scale preliminary study conducted to evaluate the feasibility of a full scale research project
Target Population
broad population to which the results of a study should be applicable
Source Population
sometimes called a sample frame, a week defined subset of individuals from the target population from which potential study participants will be studied
Sample Population
individuals from a source population who are invited to participate
Study Population
eligible participants who consent and complete required study activities
Sampling Bias
occurs when the individuals sampled for a study systematically are not representative of the source population as a whole
Census
is a complete enumeration of a population, such as a count of every resident of a country or inpatients at a particular time and area of a hospital
Nested case control study
uses the participants of a large longitudinal cohort study as the source population for both cases and controls
Eligibility Criteria
study comprise the inclusion criteria that must be present for an individual to be allowed. To participate in a study and the exclusion criteria that require an individual to be removed from study population
Vulnerable Populations
whose members might have limited ability to make an autonomous decision about volunteering to participate in a research study
Key Informants
: individuals selected to participate in a qualitative study because they have expertise relevant to the study question
Sample Size
number of observations in a data set, usually the number of individual humans in the study population
- Large samples from a population are usually better than small ones at yielding a sample mean close to the true population value
Confidence Interval
statistical estimate of the range of likely values of a parameter in a source population based on the value of that statistic in a study population
Sample size calculator
is a tool used to identify an appropriate number of participants to recruit for a quantitative study
What type of error occurs when a statistical test of data from the study population finds no significant result even though a significant difference or association actually exists in the population
Type 2 Error
Agent
pathogen or chemical or physical cause of disease/injury
Likert scale
- present ordered responses to a questionnaire item that asks participants to rank preferences numerically such as using a scale where 1 means you strongly disagree
Anonymity
- the inability of a participant’s identity to be discerned from his/her responses to a survey instrument or records in a database
Habituation
error that occurs when participants completing a questionnaire/interview become accustomed to giving a certain response (agree) That they continue to reply with the same response even when it does not match their perspective
Skip-logic
codes that can automatically hide irrelevant questions from participants based on their responses to filter questions
Cronbach’s Alpha
measure of internal consistency used with variable that have ordered responses
Expressed with a 0 or 1
Test-Retest Reliability
demonstrated when people who take a baseline assessment and then retake the test later have the same scores each time the are tested
Content validity/ Logical Validity
- present when subject matter experts agree that a set of survey items captures the most relevant information about the study domain
Face Validity
present when content experts and users agree that a survey instrument will be easy for study participants to understand and correctly complete
Construct Validity
present when a set of questions in a survey measles the theoretical construct the toolo is intended to assess
Convergent Validity
present when 2 items that the underlying theory says should be related are shown to be correlated
Back translation/ double translation
one person translates the questionnaire from the original language to a new language and then a second person translates the survey instrument in the ne language back into the original language
