Sampling Techniques PDF

BASIC CONCEPTS ON POPULATION AND SAMPLING POPULATION - The aggregate of cases in which a researcher is interested. Target Population – also called the universe, is made up of the group of people or objects to which the researcher wishes to generalize the findings of a study....

BASIC CONCEPTS ON POPULATION AND SAMPLING POPULATION - The aggregate of cases in which a researcher is interested. Target Population – also called the universe, is made up of the group of people or objects to which the researcher wishes to generalize the findings of a study. Accessible Population – is that group that is actually available for study by the researcher. ELEMENT - single member of a population Elements or members of a population are selected from a sampling frame - which is a listing of all the elements of a population SAMPLING/SAMPLE - Selection of a portion of the population (a sample) to represent the entire population. REPRESENTATIVE SAMPLE - is one whose key characteristics closely approximate those of the population. SAMPLING BIAS - The systematic over- or under-representation of segments of the population on key variables. SAMPLING ERROR - differences between population and sample values. ELIGIBILITY CRITERIA - specify criteria that define who is included in the population. CONSIDERATIONS IN ELIGIBILITY CRITERIA Costs Practical constraints People’s ability to participate in study Design considerations SAMPLING PLAN - Specify in advance how many participants are included and participants are to be selected. HOW BIG DOES THE SAMPLE NEED TO BE? THERE ARE NO SIMPLE FORMULAS THAT CAN TELL YOU HOW LARGE A SAMPLE IS NEEDED IN A GIVEN QUANTITATIVE STUDY. THE LARGER THE SAMPLE, THE MORE REPRESENTATIVE OF THE POPULATION IT IS LIKELY TO BE. THE LARGER THE SAMPLE, THE SMALLER THE SAMPLING ERROR. TOOLS IN SAMPLING SIZE - Power Analysis - Effect Size - Slovin’s Formula CONSIDERATIONS THAT AFFECT SAMPLE SIZE IN QUANTITATIVE STUDIES Homogeneity of the population Effect size (strength of relationships) Attrition (loss of subjects) Interest in subgroup analyses Sensitivity of the measures PROBABILITY AND NON-PROBABILITY TYPE OF SAMPLING QUANTITATIVE Sampling Technique Definition Probability Type of Sampling The word random describes the procedure used to select elements (participants, cars, test items) from a Simple Random Sampling population. When random sampling is used, each element in the population has an equal chance of being selected (simple random sampling). To stratify means to classify or to separate people into groups according to some characteristics, such as position, rank, income, education, sex, or ethnic background. These separate groupings are referred to Stratified Random sampling as subsets or subgroups. For a stratified random sample, the population is divided into groups or strata. A random sample is selected from each stratum based upon the percentage that each subgroup represents in the population. used in a large-scale studies where the population is Cluster (multi-stage) sampling geographically spread out. The sample is drawn from a numbered list of people. A person is randomly picked near the top of the list, Systematic Sampling then every Nth name is selected after that (Nth could be 3rd, 7th, 10th or whatever number is needed to get the correct sample size). Non-probability (FOR QUANTI AND QUALI) Convenience sampling is used because it is quick, inexpensive, and convenient. Convenience samples Convenience are useful for certain purposes, and they require very little planning. Researchers simply use participants who are available at the moment. A small group is initially identified. After data are collected from them, they are asked to identify others Snowball who might have specialized knowledge regarding the topic; those thus identified recommend others. is one in which the researcher identifies population Quota strata and demonstrates how many participants are needed for each stratum. Individuals are selected because of their expertise, Purposive specialized knowledge, or characteristics. SUB-TYPE PURPOSIVE SAMPLING TECHNIQUE FOR QUALITATIVE RESEARCH QUALITATIVE SAMPLING TECHNIQUE Definition Involves purposeful selecting cases with a wide range of variation or Maximum Variation Sampling dimensions of interest. Diverse backgrounds Deliberately reduces variation and permits a more focused inquiry Homogenous Sampling Understanding a particular group of people Provides opportunities for learning from the most unusual and Extreme (Deviant) Sampling extreme informants. outstanding and notable failures Is similar to extreme case sampling but with less emphasis on the Intensity Sampling extremes. Select rich cases that offer strong examples of phenomenon Involves the selection of participants who illustrate or highlight what is Typical Case Sampling typical or average Typical manifestation of the phenomenon being studied Involves selecting important cases regarding the phenomenon of interest Critical Case Sampling Look for good study that illuminates critical aspects of the phenomenon Involves studying cases that meet a predetermined criterion of importance Criterion Sampling Data from the quantitative component are used to select cases meeting certain criteria for in-depth study Involves the selection of people or incidents on the basis of their Theory-based Sampling potential representation of important theoretical construct Usually based on a priori theory that is being examined qualitatively FACTORS AFFECTING SAMPLING SUCCESS Method of recruitment (face-to-face, by mail, etc.) Courtesy Persistence Incentives (gifts, monetary payments) Research benefits RESEARCH INSTRUMENT - Research Instruments are measurement tools (for example, questionnaires or scales) designed to obtain data on a topic of interest from research subjects. CRITERIA FOR SELECTION OF A DATA COLLECTION INSTRUMENT The practicality of an instrument concerns its cost and appropriateness for the study population. How much does the instrument cost? How long will it take to administer the instrument? Will the population have the physical and mental stamina to complete the instruments? Will the researcher require special training? Are special motor or language abilities required? SOURCES OF INSTRUMENT Use of existing instrument - Health and Psychosocial Instruments (HAPI or HaPI) can be one of the sources of your instrument. This data base can be searched through the Ovid interface. Many of the existing instruments are copyrighted. The copyright holder must be contacted to obtain permission to use such an instrument.  Developing an instrument - If no instrument can be discovered that is appropriate for a particular study, the research is faced with developing a new instrument. - It maybe possible to revise an existing instrument. If any items are altered or deleted or new items added to an existing instrument, the reliability and validity of the toll may be altered. PILOT STUDY - One of the primary reasons a pilot study is conducted is to pre-test a newly designed instrument. - Whenever a new instrument is being used in a study or a pre-existing instrument is being used with people who have different characteristics from those of whom the instrument was originally developed, a pilot study should be conducted. - A pilot study is a small-scale trial run of the actual research project. - A fairly common number is about 10 subjects. 3-4 per item to 40-50/item (Knapp & Brown, 1995), and or 10/item (Polit and Beck, 2008) RELIABILITY - The reliability of an instrument concerns its consistency and stability. - Reliability needs to determine whether the instrument is a mechanical device, a written questionnaire or a human observer. - In general, the more items that an instrument contains, the more reliable it will be. The likelihood of coming closer to obtaining a true measurement increases as the sample of items to measure a variable increase. - Reliability is not a property of the instrument that, once established, remains forever. - Reliability must be continually be assessed as the instrument is used with different subjects and under different environmental condition. Types of Reliability Definition Stability Refers to its consistency over time Equivalence Concerns the degree to which two different forms of an instrument obtain the same results or two or more observers using a single instrument obtain the same results Internal Consistency scale of homogeneity, addresses the extent to which all items on an instrument measure the same variable. Cronbach Alpha is used to measure internal consistency VALIDITY - The validity of an instruments concerns its ability to gather the data that is intended to gather. - The greater the validity of an instrument, the more confidence you can have that the instrument will obtain data that will answer your research questions or test your research hypothesis. Types of Validity Definition Face When a cursory examination shows that it is measuring what it is supposed to measure. The validity of an instrument can be examined through the use of EXPERTS in the content area. Content Is concerned with the scope or range of items used to measure the variable that adequately measures the construct domain. How representative are the questions on this test of the universe of questions on this topic? Criterion Is concerned with the extent to which an instrument corresponds to or is correlated with some criterion measure of the variable of interest.  Concurrent Compares an instrument’s ability to obtain a measurement of subjects’ behavior that is comparable to some other criterion of that behavior. Predictive Is concerned with the ability of an instrument to predict behavior or responses of subjects in the future. Construct Is concerned with the degree to which an instrument measures the construct it is supposed to measure. RELATIONSHIP OF VALIDITY AND RELIABILITY An instrument can be reliable without being valid however, it cannot be that an instrument can be valid without being reliable. Ethics in Nursing Research UNIVERSAL ETHICAL PRINCIPLES These ethical principles include respect for persons, beneficence, and justice. These principles, what they mean, and how they are applied to research, are discussed in the following paragraphs. a. Respect for persons and communities Respect for persons and communities has everything to do with respect for their autonomy and capacity for self- determination. Respecting their capacity to decide for themselves is a reflection of the respect for the dignity of an individual. Respect for communities, on the other hand, means respect for the individuals that make up the community as well as their culture, beliefs, and practices. Special attention is given to individuals and communities, which can be considered vulnerable. b. Meaning of Beneficence Beneficence, the second universal ethical principle, means concern for the physical, mental, and social well-being of the human participants and the communities where they come from. The risk-to-benefit ratio of participation in the research must be favorable. This means that the investigators are ethically obliged to maximize the benefits that will be derived from the research while at the same time minimizing the risk that is associated with participation in the research. This obligation can be largely attained if the research design is scientifically sound, and the investigators are competent by their training and experience. The protection of the participants is the primary responsibility of the researcher. Beneficence means non- maleficence, which means to do no harm. c. Justice Justice in research is interpreted as an ethical obligation of the investigator to treat each person in accordance with what is morally right and proper. Justice in research is defined as 'distributive justice,' which means the equitable distribution of both burdens and benefits of participation in research. This also means the need for special protection for vulnerable groups. "Researchers are expected to refrain from practices that are likely to worsen unjust conditions or contribute to new inequities." (CIOMS, 2008) ELEMENTS OF THE RESEARCH ETHICS The elements of research ethics include, among others, the following — social value; informed consent; vulnerability of research participants; risks, benefits, and safety; privacy and confidentiality of information; justice; and transparency. Social value in the context of research means that the participation of human subjects in research can only be justified if the study has social value. Social value means the relevance of the study to an existing social or health problem such that the results are expected to bring about a better understanding of related issues or contribute to the promotion of the well-being of individuals, families, or communities. a. Since social value is of prime importance in research, the investigators should present/discuss the social value of his/her proposed research in at least in significance of the study, in the study design and methodology, and in the dissemination plan. In the significance of the study, the investigator should clearly describe the proposed study's significance and support his claims with an accurate and updated description of the status of the social/health problem and clearly explain how the proposed study will help address the problem. The proposed study design and methodology should be able to generate information that will support the objectives of the study. Social value can be achieved only if the study is scientifically sound. Dissemination of the study results is essential to achieving social value. The study participants and their communities should be informed about the findings of the study. Thus, a dissemination plan for the study results, as well as its intended audience during this dissemination, should be included in the research proposal. THE INFORMED CONSENT The fundamental ethical principles and their provisions are operationalized in informed consent and the process by which informed consent is obtained and documented. a. The Informed Consent (IC) is a decision of a competent potential participant to be involved in research after receiving and understanding relevant information without having been subjected to coercion, undue influence, or inducement. For participants who are incapable of giving his/her consent (or have a diminished capacity to give informed consent), the researcher must exert efforts to obtain his/her assent AND the consent of a legally authorized representative (LAR), in accordance with applicable laws. b. For participants who are incapable of giving his/her consent (or have a diminished capacity to give informed consent), the researcher must exert efforts to obtain his/her assent AND the consent of a legally authorized representative (LAR), in accordance with applicable laws. c. Informing the potential participants shall not merely be a ritual recitation (or reading) of the contents of a written document. Instead, the researcher shall convey the information, whether orally, or writing, or other modes of communication, in a language and manner that suit the individual's capacity and level of understanding. (It is generally recommended to use a language and present them in such a way that it will be understood by a Grade 6 student.) d. The researcher shall ensure that the prospective participant has adequately understood the information and that the researcher shall give each participant the full opportunity to ask questions, and should answer them honestly, promptly, and completely. Essentially, informed consent is obtained by informing the potential volunteer, by repetition and explanation, by answering their questions, by ensuring that they understand each procedure, and by obtaining their agreement to participate. Getting informed consent of the participants shows the researcher's respect for the participants' dignity and autonomy. Thus, Informed consent is a communication process between the researcher and the research participants that starts even before the research is initiated and continues throughout the duration of the study. The following are the essential information that should be given to the potential research participants (as part of the informed consent): a. That the individual is invited to participate in a research being undertaken by the researcher (name of researcher) from the institution (name of institution). If this is not made clear to the patients invited to participate in the research (e.g., clinical trials) they may think this is part of the usual care and management of patients b. Why/how the individual was chosen; c. That the person is free to refuse to participate without penalty or loss of benefits to which he/she is entitled; d. The purpose of the research, the procedures to be carried out by the researcher, and an explanation of how the research differs from routine medical or health care; e. The expected duration of the individual's participation (including the number and duration of visits to the research center) f. Any foreseeable risks, pain or discomfort, or inconvenience to the individual (or others) associated with participation in the research; g. The direct benefits, if any, to individuals who participate in the research; h. Whether money (how much) or other forms of material goods (what kind), will be provided in return for the person's participation; i. The expected benefits of the research to the community or to society at large, or contribution to scientific knowledge (i.e., indirect benefits, if any) j. Whether any intervention found to be safe and beneficial will be made available (when and how) to the research participants after they have completed their participation in the research and whether they will be expected to pay for them; k. The provisions to ensure respect for the privacy of the research participants and the confidentiality of records in which they are identified including documentation of their participation (e.g., photos, audio recording and transcripts of interviews); l. Legal or other limits to the researcher's ability to safeguard confidentiality, and the possible consequences of breaches of confidentiality; m. That participants are free to withdraw from the research at any time without having to give any reason, and without penalty or loss of benefits to which the person is entitled; n. The sponsors of the research, the institutional affiliation of the researchers, and the nature and sources of funding for the research; o. The possible research uses, direct or secondary, of the person's medical/health records, and the possible future use of biologic specimens; on storage of biologic specimens (where and for how long, and final disposition). p. Whether commercial products may be developed from biological specimens, and whether the research participant shall receive monetary or other benefits from the development of such products; q. The extent of the researcher's responsibility to ensure needed services to the research participants; r. Whether treatment and rehabilitation will be provided free of charge for specified types of research-related injury or complications associated with the research; s. That a PHREB-accredited REC has approved or cleared the research protocol; and the contact information of persons designated to respond to respond to the following — i) queries on the details of the protocol; ii) issues related to the human rights of participants; iii) related concerns and grievances; and iv) management of research-related injuries. How is the participant's consent documented? As a general rule, documentation of informed consent includes an actual signature or thumbmark of the potential participant on the informed consent form. When the use of an IC form is not feasible or unacceptable to the prospective client, a description of the process, attested by a witness, may be an alternative that needs prior approval of the REC. For instance, it will be difficult, if not impossible, to get signed informed consent for study populations that are engaged in illegal activities like illegal drug use or prostitution. VULNERABILITY OF RESEARCH PARTICIPANTS Vulnerable participants shall require special protection when they are the study population of research projects. "Vulnerable participants are those who are, relatively or absolutely, incapable of deciding for themselves whether or not to participate in a study for reasons such as physical and mental disabilities, poverty, asymmetric power relations, and marginalization, among others, and who are at greater risk for some harms." (CIOMS, 2008) Vulnerable groups shall not be included in research unless such research is necessary to promote the welfare of the population represented, and such research cannot be performed on non-vulnerable persons or groups. Caution shall be observed in obtaining informed consent for a research project if the research participant is in a dependent relationship (organizations with a hierarchical structure) with the researcher to ensure that the consent is not given under duress or undue influence. In general, vulnerable populations are composed of the following populations: a. Children b. Elderly persons c. Dependent population (e.g. subsidiary members of a hierarchical group) d. Uncomprehending subjects (e.g., mentally retarded, uneducated or illiterate, senile, linguistically disadvantaged, inebriated, unconscious, dying) e. Mentally or behaviorally disabled f. Patients in emergency rooms g. Ethnic/racial minority groups h. Homeless persons i. Nomads, refugees or displaced persons, and persons traumatized by violence j. Patients with the incurable disease k. Individuals who are politically powerless RISKS, BENEFITS, AND SAFETY Concerning potential risks, benefits, and safety related to the participants' participation in research, the following are some essential guidelines: a. Research is justified if there is a reasonable likelihood that the population, from which the participants are derived, stand to benefit from the research; b. All research involving humans shall be preceded by a careful assessment of predictable risks, burdens, and foreseeable benefits to the research participants or to others. c. Every precaution shall be taken to minimize the negative impact of the study on the research participant's well- being is it physical or psychological harm. d. Research should be conducted only if there is an acceptable positive benefit-risk ratio. e. The researcher or sponsor/funder shall endeavor to ensure the reasonable availability and accesibility of favorable research outcomes to the community. f. Where there is ethical and scientific justification to conduct research with individuals capable of giving informed consent, the risks from research interventions that do not promise the prospect of direct benefit for the individual participant, shall be no more likely to occur and no greater than the Risk attached to routine medical or psychological examination of such persons. g. Slight or minor increases in such risks may be permitted when there is an overriding scientific or medical rationale for such increases AND when the REC has approved them. Related to this, it will be useful to define the concept of minimal Risk since it is possible for the research participants to be subjected to this kind of Risk. Minimal Risk is a classification of Risk in research where the probability and magnitude of harm or discomfort anticipated in the proposed research are not greater, in and of themselves, than those ordinarily encountered in daily life or during the performance of routine physical or psychological examinations or tests. PRIVACY AND CONFIDENTIALITY OF INFORMATION a. Researchers shall adhere to the principles of transparency, legitimate purpose, and proportionality in the collection, retention, and processing of personal information (Data Privacy Act, 2012). b. Researchers must respect the participants' right to privacy. Unless required by law, the confidentiality of information shall at all times be observed. Records that link individuals to specific information shall not be released. c. Researchers shall refrain from identifying individuals or groups when the release of information about them can expose them to possible harm or stigma unless required by law. d. For some methods (e.g., FGDs), researchers cannot ensure the confidentiality of information or the anonymity of research participants. In this case, the researchers shall ensure that the nature of the study and the questions would cause minimal harm should confidentiality or anonymity be breached. e. Where there is some likelihood or opportunity for the researcher to observe the occurrence of illegal or harmful behaviors (e.g., child abuse, substance use, self-harm, or suicide ideation), the researcher shall: I. Explicitly indicate the limits of confidentiality in the informed consent process (issue of disclosure); II. Emphasize the right of the respondent to withdraw from the study or withdraw his/her data, and to refuse to answer any question; and III. Prepare a concrete and realistic protocol for reporting and referral in the event that imminent harm and/or criminal act is disclosed or discovered in the process of data collection. f. The researcher shall describe his/her data protection plan in the protocol, including the steps to be taken so that access to the data and the identities and privacy of the respondents can be protected. JUSTICE Justice means fairness, impartiality, or righteousness. In research, however, 'distributive justice' is of interest. It requires the equitable distribution of both the burdens and benefits of participation in research. The other important requirements for justice to be 'distributive' are: a. Research should not worsen existing health and social inequities; b. Individuals and communities should have access to benefits related to participation in the study. c. There should be the fair selection in the choice of study populations, sampling, and assignments; d. Appropriate care should be given to participants regardless of their economic status, gender, race or creed; e. There shall be just compensation for harms brought about by participation in research; f. Research participants should be reimbursed for lost earnings, travel costs, and other expenses incurred when taking part in the study. g. When there is no prospect for direct benefit, participants may be given a reasonable and appropriate incentive for inconvenience; h. Payments or incentives should not be too large to induce eligible participants to consent to join the study (undue inducement). TRANSPARENCY In an ethical research, the transparency means that all parties, the sponsors, the researchers and even the research participants, need to be honest and truthful in matters related to their participation in the research. Also important is for the researchers to disclose potential conflicts of interest about matters relating to their involvement in the research. Transparency in research is important for the following reasons: a. It promotes confidence in the research enterprise even when privacy and anonymity need to be preserved about sensitive matters. b. Also entails disclosure of research results. c. Researchers must be transparent about aspects of a study that may have an impact on the rights, health, and safety of participants, or with respect to information that may have a bearing on the decision of participants to give or withhold their informed consent. d. Disclosure of research results to research participants shall occur only when ALL of the following situations apply: I. The findings are scientifically valid and confirmed; II. The findings have significant implications for the participants' well-being; and III. The course of action to ameliorate these concerns is readily available when research results are disclosed to its participants. e. Transparency imposes responsibilities on researchers to disclose information about their affiliations, financial interests, or other loyalties that may affect their objectivity and the integrity of their research outputs (i.e., potential conflicts of interests) HOW THE QUALITY OF RESEARCH IS ENSURED Given the guidelines that are presented above, how can a researcher ensure that these guidelines that will protect study participants are adequately reflected in the research protocol/proposal? The requirements of an ethical research can be ensured through the following mechanisms - that the research proposal is scientifically valid; that the researchers are qualified and competent; that the research proposal underwent an ethics review by a Research Ethics Committee; that the REC is PHREB-accredited; and that the responsibilities of the relevant stakeholders are clearly specified. THE RESEARCH PROTOCOL The research protocol is the main instrument that can help ensure that proposed research will be scientifically valid and ethical sound. In essence the research protocol shall provide information on how the safety and welfare of the research participants will be protected by the investigator and everyone who will be involved in the research. The proposal can do this by: a. Providing guidance for those who will conduct the study, reference for evaluators and reviewers, template for validation, substantiation for intellectual property claims, and legacy of the proponent; As such, it should be rigorously conceptualized, carefully crafted/designed, and elegantly formulated, and clearly written. b. Being sufficiently detailed to serve as documentation of the study. c. Justifying the need for the study; d. Establishing the appropriateness of the proposed methods to investigate the research problem; e. Providing evidence for the feasibility of doing the proposed study; f. Defining the recruitment process (where, who, how); g. Describing the dissemination plan for research results and outcomes. h. Clearly describing the purpose of the study, the design, the study population, the methods of data collection and the planned analysis; i. Describing all procedures, whether invasive or not, adequately; j. Addressing the elements of research ethics adequately as part of the 'Ethical Considerations' section;