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research test 3

ch. 12 sampling plans

Sampling Plan goal: to obtain a representative group to enable generalizability in making conclusions process of selecting a portion of the population to represent the entire population ( may be humans, animals, objects, events, organizations) in a research study
where is the sampling plan most frequently found in a report? method sections
Eligibility Criteria **eligibility= inclusion **delimitations= exclusion characteristics that restrict the population to a specific group thus decreasing extraneous variables and increasing generalizability of research findings **need to indicate inclusion criteria and exclusion criteria in report
Sampling Bias overrepresentation or underrepresentation of specific segment of the population that may affect the variables of interest in a study (ex: use only Ss attending diabetes clinic; use only Ss with land line phones for surveys rather than cell phone)
non-probability sampling selection of subjects by nonrandom methods (every subject does not have an equal and independent chance of being selected) **convenience **quota **consecutive **purposive
convenience sampling -selection of subjects most readily available (accessible and easy to obtain) -most commonly used in quantitative & qualitative research -weakest d/t risk of sampling bias
examples of convenience sampling 1. first 100 students in FAMU library (many have high GPA) 2. first 20 ppl in mall (mostly female) 3. all members of a church (most have empathy level) 4. all children in a day care center (most have working parents unable to stay home)
Quota sampling **researchers identify population strata and determine how many participants are needed from each stratum selection of subjects based on predetermined strata with proportionate representation in each subgroup **stronger than convenience d/t use of homogenous groups to ensure representation
consecutive sampling selection of subjects most readily available over a specified time period or for a specified sample size **stronger than convenience d/t use of all subjects available
ex of consecutive sampling -all pts admitted to a burn unit over a 6 mo. period, all premature infants weighing less than 3 lbs in a NICU over a 6 wk period, 1st 100 patients admitted to a ED with acute asthma
purposive sampling selection of subjects based on personal judgement of researcher about who will be most typical of population **used in quantitative and qualitative research **bias may occur d/t subjective nature of being "handpicked"
ex of purposive sampling -persons with a specific disorder (Reye's syndrome), monozygotic twins raised apart to assess cardiac disease *genetic v environment influence)
Probability sampling selection of subjects by random methods (every subject has an equal and independent chance of being selected) **different than random assignment** 1. simple random sampling 2. stratified random sampling 3. cluster sampling 4. systematic sampling
simple random sampling selection of subjects via a list derived from all members of a population, then selecting a random sample from the sampling frame **most basic procedure, but often not used d/t difficulty in obtaining or compiling lists
ex of simple random sampling Ss drawn randomly from a list of all hospitals in GA with cancer units, from a list of all NPs in FL, from a list of all drivers in a county issued a DUI
stratified random sampling **the population is first divided intp 2 or more strata. As with quota sampling, the aim of stratified sampling is to enhance representativeness selection of subjects based on predetermined strata, then selecting a random sample from each subgroup (similar to quota sampling) **ex of proportional/equal
cluster sampling selection of subjects via a random sample of first a large group, then selecting from successive smaller groups
ex of cluster sampling all hospitals in florida, then region, then units with nurses caring for pts with GSWs; all high schools in florida, then region, then 11th grade classes for teenagers engaging in organized sports activities
systematic sampling selection of subjects such that every kth person in a sampling frame is selected **identify population (N= 500), decide sample size (n= 50), divide population by sample size [k= N/n or 500/50= 10th]
ex of systematic sampling patients using anticoagulant post-knee replacement following discharge, patients with HbA1C > 7 in diabetic clinic, nurses recording pain level in postpartum patients
PROBABILITY *simple random *stratified *cluster *systematic -random selection -difficult to obtain sample -more representativeness -more generalizability -less bias -more costly and time-consuming
NON-PROBABILITY *convenience *quota *consecutive *purposive -non random selection -easy to obtain sample -less representativeness -less generalizability -more bias -less costly and time consuming
sample size: quantitative study use largest number possible to ensure representativeness and generalizability; determined primarily by degree of precision desired, prevalence of problem, cost, and time *consider conducting a pilot study
pilot study trial run with few Ss to identify feasibility of study, problems with design, reliability and validity of instruments, and to refine treatment protocols and data collection procedures
sample size: qualitative study interview Ss until data saturation has occurred
sampling process 1. identify target population and accessability 2. develop sampling plan 3. determine eligibility criteria 4. determine sample size 5. obtain IRB approval 6. obtain subjects
Created by: lissy11