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Statistics, data collection and sampling Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerStatistics Statistics is a branch of mathematics mainly concerned with collection, presentation, analysis and interpretation of quantitative or numerical data. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerTwo Major Divisions of StatisticsDescriptive statistics deals with the gathering, classification, organization and presentation of data in a form that is understandable to all.It processes data without attempting to draw any inferences from it.Thus, the objective of descriptive statistical analysis is to summarize some of the important features of a set of data.Construction of tables and graphs, computations of measure of location.

Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerTwo Major Divisions of StatisticsInferential statistics is concerned with the formulation of conclusions or generalizations about a population based on an observation or a series of observation of a sample drawn from the population.This is also known as inductive statistics which is a scientific discipline concerned with the developing and using mathematical tools to make forecast and inferences.Inferential statistics requires a higher-order of critical judgment. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerMethods of Data Collection1. Direct method is often referred to as interview method. Researchers may use the structured or unstructured interviewVery expensive and time consuming but gives the researcher a more valid result.Mainly used for a small sample size. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerMethods of Data Collection2. Indirect method popularly known as the paper and pencil method or the questionnaire method.Researcher has to prepare questions relevant to the subject of his study. less expensive and requires a much shorter time but there might be a high possibility of incorrect responses Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerFeatures of a Good Questionnaire (Data Collection Instrument)1. it must be short and clear enough to be understood by the respondents.2. avoid stating a leading question.3. be precise with every statement particularly with the units to ease the tabulation of data.4. design a structured questionnaire which just be easily checked or blocked by the respondents.5. limit questions only to the essential information need in your study.6. arrangement and/or sequencing should be properly done. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerMethods of Data Collection3. Registration method others referred to this method as documentary analysis where the researcher make use of t he data/fact/ information on file.These documents are something that is enforced by a certain law or policy.This includes birth, death, licenses, and other records. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerMethods of Data Collection4. Observation method data pertaining to behaviours of an individual or a group of individuals at the time of occurrence of a given situation are best obtain by direct observation.Subjects may be taken individually or collectively, depending on the target of the investigation.Used if objects of the study cannot talk nor write.Examples are plants and animals. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerMethods of Data Collection5. Experiment method this method examines the cause and effect of certain phenomena.Data obtained here are done through a series of experiments which require laboratory results. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerScale of MeasurementThere are many types of data that we gather about:Age of respondents;Educational attainmentEmployees incomeSex of respondentsNumber of students per classWe call these as variables. Variables can be classified, measured and labeled. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerScales of MeasurementNominal Scaleuse of symbols to classify or categorize into 2 or more categoriesRefers to a property of the members of a group defined by an operations which allows making of statement of equality or differences.e.g., using numbers to categorize gender (male or female)Civil status (single, married, widower)Juices (mango juice, orange juice, apple juice) Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerScales of MeasurementOrdinal ScaleGrouped according to rank-order scale of measurementOne object or member is less or greater than the otherse.g., finishing order in a raceFood in a restaurant ( taste is excellent or poor)Winners are always ranked as 1st, 2nd, 3rd Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerScales of Measurement (cont'd)Interval ScaleShow sameness or difference of objects or whether one is less than or greater than the other but it make statement of equality of intervals.same properties of ordinal plus equal distances between adjacent numberse.g., temperature on Fahrenheit scaleStudents got scores in the test, are considered interval variables Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerScales of Measurement (cont'd)Ratio ScaleVariables where the quality of ratio or proportion is important. This time, there is a zero point.The number used represent distances from a natural origin like length, weight, height, etc.

Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerExercise: state whether the following variables is a nominal, ordinal, interval or ratio.1. price of rented house2. place of residence3. the scent of a flower4. the salary of 12 teachers5. scores in an IQ test6. grades in algebra7. the verdict of a jury8. the order of birth in the family9. the breaking strength of a certain type of cable10. the amount of water in a jug11. the number of kings in a deck of cards12. distance traveled by a car13. places in the sportsfest14. number of subdivision in Cavite15. floor area of ten classrooms Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerSampling MethodsSample a set of elements selected from a population.This is taken to mean that they represent the characteristics of a population.Population the full set of elements from which the sample was selected.The total number of people, objects or events that we consider in our study.The data obtained about a population are known as parameters. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerSampling Methods (cont'd)Sampling process of drawing elements from population to form a samplerepresentative sample equal probability method of selection method (EPSEM)Statistic a numerical characteristic of sample data Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerSampling Methods (cont'd)Parameter a numerical characteristic of population dataSampling error the difference between the value of the sample statistic and the value of the population parameterSampling frame a list of all the elements in a population Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerSampling TechniqueThere are two major sampling technique:The probability and the non-probability sampling: Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerSampling Technique1. Probability sampling is a sampling procedure wherein every element of the population is given a non-zero chance of being selected as a sample.This is taken to mean that everyone in the population has the chance to be included in the sample. It is otherwise known as random sampling. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerRandom Sampling TechniquesSimple Random SamplingSelection is done fairly, just and without bias.choosing a sample in a manner in which everyone has an equal chance of being selectedsampling without replacement is preferred random numbers generators simplify the process Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerRandom Sampling Techniques (cont'd)Stratified Random Samplingrandom samples drawn from different groups or strata within the populationproportional stratified sampling involves insuring that each subgroup in sample is proportional to the subgroups in the populationExample: No. of students enrolled in UST Faculty of Arts and Letters (total samples needed 600Comm Arts 1,300 Journalism - 375LegMa - 750 Pol. Science 195History 160 Economics - 245

Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerExercise 2: Stratified SamplingThe City of Las Pinas would like to get samples from the different Barangays on their program. The Mayor would like to have a 400 total samples for this survey.Barangay No. of ResidentsBgy.Pilar 2,567Almanza Uno 1,879Almanza Dos 3,455P. Lupa 1,988CAA 4,511BF Resort 3,257Determine the samples to be taken from each Barangay using the stratified sampling method.

Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerRandom Sampling Techniques (cont'd)Cluster Random Samplinginvolves random selection of groups of individuals (clusters)one-stage cluster sampling involves randomly selection clusters and using all individuals withintwo-stage cluster involves randomly choosing individuals within each chosen cluster Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerRandom Sampling Techniques (cont'd)Multi-stage samplingThis technique is referred to as selection of samples in several stages of sampling.How do you know the population of a certain university?How did the Philippines obtain its total population?If a candidate in senatorial election would like to conduct a mock-election, what would be done to determine approximately how many would go for him in the whole country? Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerNon-Probability Sampling Techniques It is a sampling technique wherein not every element of the population is given a chance of being selected as sample.The researcher states his prejudice for certain samples.It is otherwise known as non-random sampling. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerTypes of Non-random Sampling1. purposive sampling is a non-random technique of choosing samples where the researcher defined his criteria and rules.If you meet the criteria set, then you can be counted as part of the sample.Example: Research on shampoo only with long hair

Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerTypes of Non-random Sampling2. quota sampling the researcher or investigator limits the number of his samples on the required number for the subject of his study.3. convenience sampling the researcher chooses his most preferred location/venue where he can conduct his study.The researcher specifies the place and time where he can collect his data. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerWhich one to use: Random or Non-randomOne cannot depict what is the best technique to be applied in a particular research.The technique to be used greatly depend on the subject of the study.The techniques mentioned where by random or non-random sampling can be done in combination. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerDetermining Sample SizeIf less than 100 use entire populationLarger sample sizes make it easier to detect an effect or relationship in the populationCompare to other research studies in areaLarger sample sizes are needed if population is Heterogeneous (different) Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerDetermining Sample Size (cont'd)Larger sample sizes are needed if population is heterogeneousyou have multiple groupsif you want increased precisionwhen you expect a small effect Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerDetermining Sample Size (cont'd)Larger sample sizes are needed if population is when you use less efficient methods of samplingfor some statistical techniquesif you expect a low response rate Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerDetermining Sample SizeThere are two ways to obtain the sample size:1. By percentage methodFor a very large population, 10% of the population is obtained.For a small population, 20% of the population is desired.This rule is arbitrary and depends on the researcher. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerDetermining Sample Size`2. By margin of error method or Slovins FormulaIf a researcher wants to have 95% precision in the result of his study, that would implicate a margin of error of 5%. Thus the following formula shall be applied: n = ___N___ 1 + Ne

2n= sample sizeN = population size e = margin of error Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerExercise 3: Margin of ErrorHow many samples must be obtained from 20,000 UST students if a 5% margin of error is used? Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerExercise 3: Margin of ErrorAnswer: 392 students

Therefore, it requires 392 UST students as samples using 5% margin of error from 20,000 population. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerExercise 4: Margin of Error1. How many samples must be obtained from 120,000 population if the margin of error is set at 10%.?

2. Using a precision rate of 93.5% how many samples must be obtained with a 754,000 population? Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson TurnerSampling in Qualitative ResearchQualitative research focuses on in-depth study of one or a few cases.Several different sampling methods are available. It is common to mix several different methods. Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson Turner

Copyright 2011 by Pearson Education, Inc.All rights reserved.Research Methods, Design, and Analysis, Eleventh EditionChristensen Johnson Turner