Formulation of the Research Methods
Selecting the Appropriate Design Selecting the Subjects Selecting Measurement Methods & Techniques Selecting InstrumentationWhat is research?
* “Scientific research is systematic, controlled, empirical, and critical investigation of natural phenomena guided by theory and hypotheses about the presumed relations among such phenomena.” Research is an organized and systematic way of finding answers to questionsFormulation of the Research Methods
Developing Procedures & Protocol Using a Pilot Study Selecting the Appropriate Analysis Techniques Developing a Timeline & Budget Collecting the DataSampling Procedures
DefinitionsPopulation – group of things (people) having one or more common characteristicsSample – representative subgroup of the larger populationUsed to estimate something about a population (generalize)Must be similar to population on characteristic being investigated
Representative
SAMPLING……. * 3 factors that influence sample representative-nessSampling procedureSample sizeParticipation (response)When might you sample the entire population?When your population is very smallWhen you have extensive resourcesWhen you don’t expect a very high response
* SAMPLING BREAKDOWN
Sampling MethodsProbability Sampling Simple random sampling Stratified random sampling Systematic sampling Cluster (area) sampling Multistage sampling
Non-Probability Sampling Deliberate (quota) sampling Convenience sampling Purposive sampling
Simple Random Sampling
Equal probability Techniques Fishbowl (with replacement & w/o replacement) Table of random numbers Advantage Most representative group Disadvantage Difficult to identify every member of a populationStratified Random Sampling
Technique Divide population into various strata Randomly sample within each strata Sample from each strata should be proportional Advantage Better in achieving representativeness on control variable Disadvantage Difficult to pick appropriate strata Difficult to ID every member in populationSystematic Sampling
Technique Use “system” to select sample (e.g., every 5th item in alphabetized list, every 10th name in phone book)Advantage Quick, efficient, saves time and energyDisadvantage Not entirely bias free; each item does not have equal chance to be selectedSystem for selecting subjects may introduce systematic errorCannot generalize beyond pop actually sampledCluster (Area) Sampling
Randomly select groups (cluster) – all members of groups are subjectsAppropriate when you can’t obtain a list of the members of the population have little knowledge of pop characteristicsPop is scattered over large geographic area
Cluster (Area) Sampling
Advantage More practical, less costlyConclusions should be stated in terms of cluster (sample unit – school)Sample size is # of clustersMultistage Sampling
Stage 1 randomly sample clusters (schools) Stage 2 randomly sample individuals from the schools selectedSampling Methods
Probability Sampling Simple random sampling Stratified random sampling Systematic sampling Cluster (area) sampling Multistage samplingNon-Probability Sampling Deliberate (quota) sampling Convenience sampling Purposive sampling
Deliberate (Quota) Sampling
Similar to stratified random sampling Technique Quotas set using some characteristic of the population thought to be relevant Subjects selected non-randomly to meet quotas (usu. convenience sampling) Disadvantage selection bias Cannot set quotas for all characteristics important to studyConvenience Sampling
“Take them where you find them” - nonrandom Intact classes, volunteers, survey respondents (low return), a typical group, a typical personDisadvantage: Selection biasUse post hoc analysis to show groups were equal at the startPurposive Sampling
Purposive sampling (criterion-based sampling)Establish criteria necessary for being included in study and find sample to meet criteriaSolution: ScreeningUse random sampling to obtain a representative sample of larger population and then those subjects that are not members of the desired population are screened or filtered outEX: want to study smokers but can’t identify all smokers
Sample Size
Critical factor is whether sample is representativeNecessary sample size depends on population size Recommendations:Use tables from books30 per groupDescriptive studies – 10-20% of populationNo more than 50% of populationStatistical powerAttritionWhen Selecting Subjects … Are subjects with special characteristics necessary for your research? (age, gender, trained/untrained, expert/novice, size, etc.) Can you obtain the necessary permission and cooperation from the subjects? Can you find enough subjects? Interaction among selection of subjects, treatments, and measures is essential for experimental studies.