Hướng dẫn triển khai thực hiện một nghiên cứu khoa học sức khỏe (tiếp)

GS TS BS LÊ HOÀNG NINHNGHIÊN CỨU LÀ GÌ ?Research is the systematic collection, analysis and interpretation of data to answer a certain question or solve a problemIt is crucial to follow cascading scientific steps when conducting one’s researchQui trình một nghiên cứu khoa họcSelection of areaSelection of topicCrude research question no answerRefined research questionResearch hypothesis, goals and objectivesStudy designPopulation & samplingVariables confounding biasResearch toolsPilot studyWork planCollection of dataData managementInterpretationReporting no need for studyanswers foundLiterature reviewEthical issues1. Thiết kế nghiên cứu Descriptive studies Analytical studies Case reportCase serialreportsCross-sectionalstudiesEcological studiesObservational studiesExperimentalstudiesCase-controlstudiesCohort studiesProspectiveRetrospective(historical)RandomizedControlled ClinicaltrialsRandomizedControlled fieldtrialsNon-randomizedexperimentsChọn lựa thiết kế tốt nhất Purpose of the studyState of existing knowledge (in relation to study question)Characteristics of the study variablesLatencyFeasibility Mục đích nghiên cứuStudy of etiology:EcologicCross-sectionalCase-controlCohortInterventionStudy of therapy:Lab experimentsClinical trialsCommunity interventionHiện trạng các kiến thức hiện có về câu hỏi nghiên cứu ?New idea:EcologicCross-sectionalNew hypothesis:Cross-sectionalCase/ case series reportNewly claimed association:Case-control: replication, confirmationCohort: stronger evidence towards causationConfirmed association:Experiment/intervention: to prove causationĐặc điểm các biến số nghiên cứuVery rare exposures: case-control design is NOT suitable since it looks for exposure. A very large number of subjects is required.Very rare disease: cohort design is NOT suitable since it looks for outcome. Follow-up of a huge number is required.Acute disease: prevalence studies are not suitableRisky exposures: clinical trials are unethicalUnavailable data: record-based studies are not suitable. Latency For diseases with very long latency, the costs of concurrent cohort studies or clinical trials are prohibitively high.Tính khả thi Time ManpowerEquipmentMoney 2. Quần thể và mẫuSampling is the process of selection of a number of units from a defined study population.Tiến trình lấy mẫu:Identification of study populationDetermination of sampling populationDefinition of the sampling unitChoice of sampling methodEstimation of the sample sizeXác định quần thể/ dân số trong nghiên cứuThe study or target population is the one upon which the results of the study will be generalized. It is crucial that the study population is clearly defined, since it is the most important determinant of the sampling populationXác định quần thể / dân số lấy mẫuThe sampling population is the one from which the sample is drawn. The definition of the sampling population by the investigator is governed by two factors:Feasibility: reachable sampling populationExternal validity: the ability to generalize from the study results to the target population.Định nghĩa đơn vị lấy mẫuThe definition of the sampling unit is done by setting: Inclusion criteriaExclusion criteria(exclusion criteria are not the opposite of inclusion criteria) Chọn lựa phương pháp lấy mẫuNon probability sampling Probability samplingLấy mẫu không xác suất:Types of non probability sampling:Convenience samplingQuota samplingLấy mẫu xác suất“There is a known non-zero probability of selection for each sampling unit”Types:Simple random samplingSystematic random samplingStratified random samplingMulti-stage random samplingCluster samplingMulti-phase samplingLấy mẫu ngẫu nhiên đơnIn this method, all subject or elements have an equal probability of being selected. There are two major ways of conducting a random sample. The first is to consult a random number table, and the second is to have the computer select a random sample. Lấy mẫu ngẫu nhiên hệ thốngA systematic sample is conducted by randomly selecting a first case on a list of the population and then proceeding every Nth case until your sample is selected. This is particularly useful if your list of the population is long. For example, if your list was the phone book, it would be easiest to start at perhaps the 17th person, and then select every 50th person from that point on. Lấy mẫu phân tầng In a stratified sample, we sample either proportionately or equally to represent various strata or subpopulations. For example if our strata were cities in a country we would make sure and sample from each of the cities. If our strata were gender, we would sample both men and women. Multistage samplingCountryProvinces Cities Districts Households Person Lấy mẫu cụmIn cluster sampling we take a random sample of strata and then survey every member of the group. For example, if our strata were individuals schools in a city, we would randomly select a number of schools and then test all of the students within those schools. Multi-phase samplePopulation Sample Sub-sampleTest 1Test 2Ước lượng cỡ mẫu“how many subjects should be studied?”The sample size depends on the following factors:I. Effect sizeII. Variability of the measurementIII. Level of significanceIV. Power of the study I. Effect size“magnitude of the difference to be detected” A large sample size is needed for detection of a minute difference. Thus, the sample size is inversely related to the effect size.II. Khả năng thay đổi do công cụ đo The variability of measurements is reflected by the standard deviation or the variance. The higher the standard deviation, the larger sample size is required. Thus, sample size is directly related to the SDIII. Mức ý nghĩa:Relies on α error or type I error. The maximum level of α has been arbitrarily set to 5% or 0.05. Alpha error can be minimized to 0.01 or even 0.001 but this consequently increases the sample size. Thus, sample size is inversely related to the level of α error.IV. Lực của nghiên cứu:The power of the study is the probability that it will yield a statistically significant result. It is related to β error or type II error. Power is equal to (1- β), consequently the power of the study is increased by decreasing the beta error. Thus, sample size is inversely related to the level of β error or directly related to the power of the study. 3. Thu thập dữ liệuData collected are “variables”Variables are classified according to their:Type:Định lượng (continuous, discrete)Định tính ( ordinal, nominal)Role in the study:DependentIndependentRelationship with other study factors:Main study variablesConfounding variablesEffect modifiersIntermediate factorsPhương pháp thu thập dữ liệu (research tools) Selection of the suitable technique depends on:The availability of informationThe type of dataThe resources availableThe characteristic of the toolCông cụ nghiên cứu Most important techniques:Using available information (records)Observation (checklist)Self-administered questionnaireInterviewing (individual/group)Measuring (all lab tests and other investigations)Chọn lựa format cho bộ câu hỏiFixed alternativeYes/NoReliableNot powerfulLikertOpen-endedMay not be properly answeredMay be difficult to scoreChọn lựa format cho bộ câu hỏi (t.t)UnstructuredInterviewer bias is a serious problemData may not be hard to analyzeSemi-structuredFollow-up questions allowedProbably best for pilot studiesStructuredStandardized, reducing interviewer bias 9 sai lầm cần tránh1. Avoid leading questions2. Avoid questions that invite the social desirability bias3. Avoid double-barreled questions4. Avoid long questions5. Avoid negations6. Avoid irrelevant questions7. Avoid poorly worded response options8. Avoid big words9. Avoid ambiguous words & phrases Các sai lệch Definition of “error”:“A false or mistaken result obtained in a study or an experiment” John last, 2001.Types of errors:Systematic error: bias:“ an error having a certain magnitude and direction repeated with every measurement”Random error:“ error with no fixed pattern of magnitude or direction” Nguồn sai lệch Sources of errors:SubjectObserverinstrumentBias Design Bias Information Bias(observer bias) sample biasStudy selection biasResponse biasInterviewer biasMeasurement bias(intra and inter obs. Bias)Reporting biasRecall biasTechnical biasSai lệch do thiết kế Selection biasSelection bias is a distortion of the estimate of effect resulting from the manner in which the study population is selected. This is probably the most common type of bias in health research, and occurs in observational, as well as analytical studies (including experiments).a. Prevalence-incidence biasThis type of bias can be introduced into a case-control study as a result of selective survival among the prevalent cases. In selecting cases, we are having a late look at the disease; if the exposure occurred years before, mild cases that improved, or severe cases that died would have been missed and not counted among the cases.b. Admission rate (Berkson’s) bias This type of bias is due to selective factors of admission to hospitals, and occurs in hospital-based studies. The diseased individuals with a second disorder, or a complication of the original disease, are more likely to be represented in a hospital-based sample than other members of the general population. Differential rates of admission will be reflected in biased estimates of the relative risks.Non-response biasThis type of bias is due to refusals to participate in a study.The individuals who do not participate are likely to be different from individuals who do participate. Non-respondents must be compared with respondents with regard to key exposure and outcome variables in order to ascertain the relative degree of non-response bias.Ascertainment or information bias Information bias is a distortion in the estimate of effect due to measurement error or misclassification of subjects according to one or more variables. Measurement biasObserver variation biasIntra-observer variationInter-observer variationSubject (biological variation)Technical method error variationSai lệch nhớ lại (Recall bias)An error of categorization may occur if information on the exposure variable is unknown or inaccurate.The recall by both cases and controls may differ in both amount and accuracy. Cases are more likely to recall exposures, especially if there has been recent media exposure on the potential causes of the disease.Example: In questioning mothers whose recent pregnancies had ended in fetal death or malformation (cases), and a matched group of mothers whose pregnancies had ended normally (controls), it was found that 48% of the former, but only 20% of the latter reported exposure to drugs. 4. Kế hoạch làm việc “State in specific steps what exactly will be done” Method: Listing the activities related to the study (planning, implementation, results)Identification of the responsibility for each activitySetting time and date for achievement of each activityPutting all these elements together in a legible form which could be a chart (GANNT chart) or a tableBudget and any funding agencies Công việc hành chính Administering the ResearchInformed consentClear instructionsDebriefingConfidentiality5. Xử lý / phân tích dữ liệu  Data management Data management is the whole process of dealing with data from the very beginning of the study. Data analysis is just the last part of it.It can be divided into the following phases:Preparation of data entryData entryData analysis Preparation for data entry:Review of questionnaire formsUnique I identifierCodingPreparation of master-sheets (manual) or spread-sheets (computer) Dummy tablesQuality controlData entryPhân tích dữ liệu:Descriptive:Tabular presentationFrequency distribution tablesCross tabulations Graphic presentation:Bar chartsPie chartsLine graphsOthersNumeric presentation:Percentages and percentilesMeasures of central tendencyMeasures of dispersion Phân tích dữ liệu ( t.t)Analytic: The researcher uses principles of biostatistics to test his hypothesis. Detection of proper statistical test depends on:The objective of the study:DescriptiveLooking for a differenceLooking for an associationType of variable:QTQLDistribution of the variable:NormalBinomialPoissonothers6. Lý giải kết quả Discussion of the results in a way that relates data obtained to each other clarifying the associations and other findings.7. Reporting comes next.