Quiz 2: Research Subjects

define target population

the total group of interest (all the of the individuals the results should apply to)

define accessible population

potential subjects who are available for study (haven’t yet consented to study)

define subjects

individuals selected from the accessible population that will participate in the research study (who consented)

define sample

subgroup individuals taken from the population (ie a group of subjects)

what are the 3 design steps that affect study success and quality (and their usefulness, believability, and relevance of the research project)?

identification of potential subjects, selection of appropriate number from the available population, and management of the subjects’ role and activities during the study

what is inclusion criteria for identifying subjects?

based on the study eligibility, is broad enough to maximize the sample size and narrow enough to minimize extraneous influence

what is the exclusion criteria for identifying subjects?

based on the study ineligibility, specify the extraneous factors that are anticipated to influence the outcome

how can subjects be located?

through a sampling frame in which you look through various sources that have lists of potential subjects in the accessible populations, or through recruiting in which there is advertisement, direct solicitation, and word of mouth to reach potential subjects.

what is sampling bias?

occurs when sampling methods produce results that systemically deviate from the truth

what is a probabilisitic sampling method?

a sampling technique in which there is random selection method for use in quantifiable research

what is a non-probabilistic sampling method?

a sampling technique that does not involve a random selection process

what is sampling error?

when a sampling method results in the chance that the sample may be different than the population for which it is drawn, or that one sample may be different from another even if they are both drawn from the same population in the same manner

what are the types of probabilistic sampling methods?

simple random sample, systematic sampling, stratified random sampling, and cluster sampling

what are non-probabilistic types of sampling methods?

convenience sample, snowball sample, and purposive sampling

describe simple random sampling?

each member of the population has an equal chance of being selected for the sample, the selection of the subjects is independent of another with each pop member assigned a number or through random numbers table or generator used to select people

describe systematic sampling

method in which every “nth” subject on sampling frame is selected, the starting point is chosen via a random number table or generator

describe stratified sampling

a method that divides the population into subgroups (strata) based on non overlapping stratification criteria, then a random sample is taken from each stratum to ensure representation. this ensures that certain subgroups are represented in an adequate numbers

describe cluster sampling

a probabilistic sampling method in which subjects are randomly selected from naturally occurring pockets of the population that are geographically dispersed

describe convenience sampling

non-probabilistic sampling method in which there is use of readily available subjects (consecutive convenience sampling is used in a prospective trial)

describe snowball sampling

non-probabilistic sampling methods in which subjects are recruited by other subjects who have already been recruited. used when potential members of the population may be difficult to identify

describe purposive sampling

non-probabilistic sampling that uses handpicked subjects that meet the researchers needs, often used in qualitative research

what is allocation?

subject assignment, primary goal is to create study groups that are equally representative of the entire sample, and secondarily to create groups of equal size, can occur randomly or non-randomly, though randomly is preferred even if the sample was selected via a non-randomized process

describe the difference between by individual and by block subject assignment/allocation

by individual randomly assigns each individual to a group, may result in uneven groups sizes which may be problematic with small sample sizes whereas by block there is a predetermined number of subjects to be contained in each group, and each member gets assigned a number and is allocated to a group in a way that maintains balance, ensuring even group sizes.

describe systemic assignment

random assignment method in which sample members are counted off or are numbered repetitively according to group numbers, those with number 1 go to group 1, those with number 2 go to group 2, etc

describe matched assignment

random assignment in which subjects are matched or formed into subsets based on important characteristics, members of those subsets are then randomly assigned to groups (kinda like stratified)

describe consecutive assignment

random assignment in which there is randomly assigned order of group assignment before subjects are enrolled in the study, as the subjects enroll, they are assigned according to the previously composed lists, this is good for using when subjects are recruited over longer time period and can’t wait to start the study for all subjects to be recruited

what are some other subject management tactics?

protocols, training and practice of the research team, maintenance of current routines, masking (blind- don’t tell the subjects which group they are in, control or treatment), discussion or interaction restrictions (instruct subjects to not discuss their study participation during the study period)

describe non random assignment

subjects are often members of preexisting groups of interest, commonly seen in retrospective studies, group assignment is determined by the presence or absence of characteristic of interest, statistical analysis tests are used ot adjust for variation due to nonrandom assignment

what is sample size and how is it important?

sample size refers to the number of subjects in a sample, and is needed to ensure statistical differences can be detected. accurate power calculations provide the minimus number needed, larger samples tend to be more representative of the population compared to smaller samples

what can insufficient sample size result in?

statistical errors (type II error- false negative)