Article Versions
Export Article
Cite this article
  • Normal Style
  • MLA Style
  • APA Style
  • Chicago Style
Research Article
Open Access Peer-reviewed

Research Process, Study Variables, Statistical Validations, and Sampling Methods in Public Health Related Research: An Update

Venkataramana Kandi
American Journal of Biomedical Research. 2022, 10(1), 1-8. DOI: 10.12691/ajbr-10-1-1
Received February 27, 2022; Revised March 28, 2022; Accepted April 05, 2022

Abstract

Scientific research is a systematic process that involves a research question, appropriate methodology, participant selection, collection of data, processing/analysis of the data using statistical applications, and finally deriving conclusions. Most public health research-related study conclusions are utilized to the betterment of the people and therefore such research is considered as evidence upon which health-related decisions are taken by the governments. In this review, we discuss the most influential aspects of the research including the research process, study variables, statistical validations, and sampling methods.

1. Introduction

The research proposal is a document that is prepared by an individual who envisages conducting it. A research proposal consists of all the necessary details of a research project that is intended to be carried out. It generally serves as a blueprint for research and is intended to gain the confidence of the sponsors, institutional review boards, and other stakeholders in the research. The three important elements which are needed to be satisfied while writing a research proposal include what do you want to achieve (answer to a research problem), why is this research being conducted (purpose), and how do you want to do it (methodology).

The essential components of a research proposal in the serial order include the title, the abstract, introduction, objectives, variables, hypothesis/research question, and methodology as shown in Table 1 1, 2.

The titles can be descriptive, declarative, and interrogative. The descriptive titles reveal the important elements of research that may include the subjects involved. Such titles however do not reveal the results and conclusions. The declarative titles may include the findings of the study and conclusive evidence. The interrogative titles appear to be inquisitive to the readers and include a research question within the title, however, they are least preferred 3.

Titles may also be compound in nature wherein the main title is followed by a subtitle that may be separated by a colon (:). Compound titles provide the readers with some specific elements of the research like the geographical areas researched, among others 4. Journal articles with inappropriate titles may be at threat to being ignored by the readers and therefore may receive less attention 5. The titles should preferably be informative and concise 6.

The need for a research proposal germinates from the necessity of an individual to prove his/her ability to carry out work or a project in a well-planned procedure. This will enforce the confidence of the peers in the researcher. The research proposals may be invited or unsolicited, wherein the researcher submits them for approval from a sponsoring body. Traditionally, most research proposals are based on academic requirements, which are necessary to acquire degrees like undergraduate, postgraduate, or doctoral degrees 7.

2. Design and Format of Research Proposals

To develop a research proposal, a researcher must be motivated. There are several basic requirements involved in the development of a research proposal. These include formulating the working topic, defining the research title, identifying the purpose of research, and the potentially interested parties concerning the area of research, performing pilot/preliminary work, cornering a research question and working out a clear plan as shown in Figure 1 8.

A research proposal is a concise document that delineates the most significant elements of the research that includes the title of the research, introduction, background information, problem statement, hypothesis, aims, and objectives, the methodology that includes details of the study period, design, sampling methods, methods of data analysis, ethical clearances, financial considerations like the budget, sponsors, and references as shown in Figure 2.

Currently, there are scarce recommendations and guidelines regarding the preparation of a quality research proposal. The most important aspect before preparing a research proposal is the careful review of the literature. This allows the researcher to understand the current knowledge, identify the gaps, and build on it 9.

3. Study Variables that Interfere with Research Results and Observations

A variable is an element, aspect, or factor of investigation in research that is bound to changes. The variables included in the study that vary or change depending on certain research/experimental factors are called dependant variables. The dependent variables are generally associated with the study participants and are usually perceived as effects enforced by the changes in independent variables. However, the independent variables are those aspects that don’t change based on the experimental reasons and alterations in the other variables included in the study. In most instances, the independent variable is potentially the cause for changes in the dependant variables.

The independent variables are also called exploratory, predictor, and right-hand-side variables. They may be experimental variables (drug composition in a clinical trial) and subject variables (gender, education, income, etc.) wherein the former ones are manipulated by the researcher whereas the latter cannot be changed.

A variable that could influence both the dependent and independent variables is called a confounder variable. A confounding variable may be considered as an extra variable that influences the research result unexpectedly. The confounding variable is related to both the dependent and independent variables. The interference of a confounding variable/s may result in bias and increased variance.

The confounding variables in a research study may cause either underestimation or overestimation of the research hypothesis. The effects of the confounding variables on the study may be neutralized by choosing random sampling, selection of subjects of different categories, and counterbalancing by dividing study subjects into groups based on specific conditions 10, 11. In a research study that attempts to find the cause-and-effect association, the confounding variables may influence the outcome, which is rather completely unexpected as shown in Figure 3.

3.1. Measurement Variables

A variable that is measured usually in numbers is called a measurement variable. The measurement variables represent the quantitative assessment of the research parameters like the activities of blood urea, and creatinine to estimate the kidney function, height of a subject, and others. The measurement variables can be of various types that include nominal variables (name, sex, etc.), ordinal variables (very satisfied, satisfied, etc.), interval variable (time, temperature, etc.), and ratio variables (multiple-choice questions, survey questionnaires, etc.) 12.

3.2. Types and Effects of Variables

The confounding variable may show two types of effects on the study. In the positive confounding, the researcher notices a significant correlation/association negating the null hypothesis. The negative confounding ignores the association and supports the null hypothesis. Also, the confounding variables can be controlled by using measures like randomization, matching, and statistical control as shown in Figure 4 10.

3.3. Control of Confounding Variables

The unmeasured variables that influence the study variables and falsely implicate cause (independent variable) and effect (dependant variable) relationships are designated as confounding variables. The researchers pursuing the study should carefully assess the potential role of confounding variables that consequently influence the validity of research results. The confounding variables are generally extraneous in origin and may be related both to dependant and independent variables. The effects of confounding variables influence the internal validity of the research. Therefore, researchers must take care of these variables and control their influence to increase the strength and validity of the study results 13, 14, 15. Methods to minimize the effects of confounding variables on the research studies are discussed further in later sections.


3.3.1. Randomization

Most clinical trials use this process to remove bias, and this includes two groups, one taking the drug and the other receiving the placebo/blank.


3.3.2. Matching

The importance of the study can be obtained, and the confounding variables are identified and neutralized by using the matched studies that include the case-control studies.


3.3.3. Statistical Control

Using multivariate analyses will neutralize the effect of confounding variables. There are a few statistical methods that can be used to minimize the effects of the confounding variables 11. This includes stratification and standardization of the study groups to fix the level of confounders 16, 17. The Analysis of Covariance (ANCOVA), linear regression, and logistic regression are multivariate statistical applications when used to analyze the results could improve the strength of the study 16.

4. Types and Characters of Study Validity

The validity of study results increasingly depends on various aspects that include bias. Moreover, study bias can be of different types including selection bias, information bias, and confounding bias. Therefore, a deep understanding of the factors that influence study validity is important while conducting research 18. The study validity includes both internal and external validity. The internal validity ensures neutralization of confounding factors, and the external validity confirms rationalization of study results on generalized terms 19. The activities of confounding factors assume increased significance in studies related to public health where the cause and effect are considered while screening people and managing and treating patients 20, 21, 22, 23.

A statistical spatial model was recently proposed to confirm the association of disease with the incidence in a particular geographical region. The researchers must assess the spatial variability and associated confounding factors during epidemiological surveillance studies to increase the study validity 24, 25, 26. Host variables those influence the microbiota-related studies that attempt to relate gut microbiota with human disease must be carefully considered 27. Different types of study validity are discussed in the following sections.

4.1. Content Validity

Content validity refers to the ability of an instrument to measure/function in ways it was designated to do. Content validity enables us to accept the results of the instrument and make decisions regarding the interpretation of the results 28. Since most instruments/machines are used in the treatment of patients, it is important that these are validated. In a previous study, the Innovative dementia-oriented Assessment (IdA®) instrument was checked at the scale-level (S-CVI) and item-level (I-CVI), for its reliability in analyzing the abnormal behavior of the dementia patients 29. Example: Instrument, and method validation for reliability, validity, and completeness.

4.2. Criterion Validity

Also called criterion-related validity, it is a measure that can predict the outcome for another one and can be compared to the gold standard. Criterion-related validity is performed by testing a novel measurement method and comparing it with the standard method or an independent criterion. This is also called concurrent validity which is done simultaneously (present), in the past, or in the future 30. Example: Validating the responses of the subjects in relation to a voting process.

4.3. Construct Validity

Construct validity is like external validity. Construct validity refers to the extent to which the research results can be generalized. It helps the researcher to validate the reliability of the questionnaire to test the research hypothesis in generating the study results. There are two types of construct validities that include convergent and discriminant construct validities. The former helps the researcher to test the relatedness between the construct and a related measure. The discriminant construct validity coveys the relatedness between the construct and unrelated measure 31. Example: Measuring the emotional maturity of the children in relation to the educational program.

5. Types of Sampling Methods

Sampling is a process of identifying a defined number of subjects from a large population to be recruited into a research study 31, 32. Good knowledge of sampling methods is essential to conduct quality research 33, 34, 35, 36. A study sample is a representation of a specific number of individuals from a large population. Sampling is a prerogative and because not all individuals participate in a research study, sample defines the representative study group that defines the characteristics of a given population as shown in Figure 5.

There are different types of sampling methods that include probability, and non-probability sampling.

5.1. Probability Sample

The probability sampling method is routinely used in quantitative research where each person in the representative population is given an equal chance of being included in the study. It is divided into four types that include simple random sampling, systematic sampling, stratified sampling, and cluster sampling.


5.1.1. Simple Random Sample

Simple random sampling gives equal chance for everyone in the population to get selected. It may use the random number generator for selecting the study participants.


5.1.2. Systematic Sample

Systematic sampling allows the researcher to select the study subjects based on the pre-defined order (1, 3, 5, 7, 9…), after assigning the potential subjects a serial number (1-100).


5.1.3. Stratified Sample

Stratified sampling is used when the population from which the sample must be taken is represented by varied characteristics. The population is separated into groups/strata based on the characteristics like age, sex, and others. Later, by using either the simple random or systematic method, the samples are selected from each group.


5.1.4. Cluster Sample

Cluster sampling involves the creation of groups of the representative population consisting of mixed characters. Since the group has mixed characteristics, each group can be considered as a sample, or a sample can be generated by using simple random/systematic sampling techniques.

5.2. Non-probability Sample

In a non-probability sampling method, the subjects are selected on a non-random criterion. Here the subjects do not have an equal chance to get selected. The non-probability sampling method, although, appears to be cheap, and easy to do, results in selection bias. Such type of sampling method is routinely used in exploratory, and qualitative research. It is suitable to perform a pilot study that is performed to understand the qualities of a small group of subjects. The non-probability sampling is of four types that include convenience sampling, voluntary response sampling, purposive sampling, and snowball sampling.


5.2.1. Convenience Sample

This sample includes only those subjects who are easily available for the researcher and has no pre-defined criteria. Although it is an inexpensive method, the results generated from studies including convenience sampling may not reflect the character of the population, and therefore, results cannot be generalized.


5.2.2. Voluntary Response Sample

In this a type of sampling method, the subjects themselves volunteer to participate in the study. Such type of sampling method is like convenience sampling and leaves enough room for bias.


5.2.3. Purposive Sample

In this sampling method, the researcher selects the sample based on his/her judgment. Elucidating the characteristics (opinions/experiences) of the specific population group. An example of such a sampling method is the handicapped group’s opinion on the facilities at an educational institute.


5.2.4. Snowball Sample

This type of sampling method is done to find the appropriate study participants based on the recommendations of the already participating subjects 37.

6. Conclusions

Research is a tedious process that is generally envisaged by the investigators to find out a solution to a problem. However, research activity involves scrupulous planning and financial support in the form of funding. The research studies, especially in the health sector include human participants and therefore it may potentially be plagued by bias and other confounding factors. Also, the research results derived conclusions are translated into human applications. This puts increased importance on the validity of the study results, and their generalizability and external validity. Considering the significance of the research conclusions, researchers and other people involved in research processes are required to have a basic and good knowledge of the research process, roles of confounding variables, cause for bias, study validity, and sampling methods as discussed in brief in this review.

References

[1]  Al-Riyami A. How to prepare a Research Proposal. Oman Med J. 2008; 23(2): 66-69.
In article      
 
[2]  Al-Shukaili A, Al-Maniri A. Writing a Research Proposal to The Research Council of Oman. Oman Med J. 2017; 32(3): 180-188.
In article      View Article  PubMed
 
[3]  Tullu MS. Writing the title and abstract for a research paper: Being concise, precise, and meticulous is the key. Saudi J Anaesth. 2019; 13(Suppl 1):S12-S17.
In article      View Article  PubMed
 
[4]  Bahadoran Z, Mirmiran P, Kashfi K, Ghasemi A. The Principles of Biomedical Scientific Writing: Title. Int J Endocrinol Metab. 2019; 17(4): e98326. Published 2019 Oct 22.
In article      View Article
 
[5]  Kumar A. Uneasy is the journey of publication that wears an inappropriate title. J Indian Soc Periodontol. 2021; 25(6): 459-460.
In article      View Article  PubMed
 
[6]  Forero DA, Lopez-Leon S, Perry G. A brief guide to the science and art of writing manuscripts in biomedicine. J Transl Med. 2020; 18(1): 425. Published 2020 Nov 10.
In article      View Article  PubMed
 
[7]  Zouaoui M. The Importance of Research Proposal https://www.univ-sba.dz/med_dialogue/images/Article.8/23.pdf.
In article      
 
[8]  Steps in Developing a Research Proposal https://courses.lumenlearning.com/ivytech-engl112/chapter/steps-in-developing-a-research-proposal/.
In article      
 
[9]  Sudheesh K, Duggappa DR, Nethra SS. How to write a research proposal?. Indian J Anaesth. 2016; 60(9): 631-634.
In article      View Article  PubMed
 
[10]  Confounding Variable: Simple Definition and Example https://www.statisticshowto.com/experimental-design/confounding-variable/.
In article      
 
[11]  Confounding variables http://www.biostathandbook.com/confounding.html.
In article      
 
[12]  Nominal, Ordinal, Interval & Ratio Variable + [Examples] https://www.formpl.us/blog/nominal-ordinal-interval-ratio-variable-example.
In article      
 
[13]  van Maaren, M.C., le Cessie, S., Strobbe, L.J.A. et al. Different statistical techniques dealing with confounding in observational research: measuring the effect of breast-conserving therapy and mastectomy on survival. J Cancer Res Clin Oncol 145, 1485-1493 (2019).
In article      View Article  PubMed
 
[14]  Groenwold RHH, Dekkers OM. METHODOLOGY FOR THE ENDOCRINOLOGIST: Basic aspects of confounding adjustment. Eur J Endocrinol. 2020 May; 182(5): E5-E7.
In article      View Article  PubMed
 
[15]  Lederer DJ, Bell SC, Branson RD, et al. Control of Confounding and Reporting of Results in Causal Inference Studies. Guidance for Authors from Editors of Respiratory, Sleep, and Critical Care Journals. Ann Am Thorac Soc. 2019 Jan; 16(1): 22-28.
In article      
 
[16]  Skelly AC, Dettori JR, Brodt ED. Assessing bias: the importance of considering confounding. Evid Based Spine Care J. 2012; 3(1): 9-12.
In article      View Article  PubMed
 
[17]  Pourhoseingholi MA, Baghestani AR, Vahedi M. How to control confounding effects by statistical analysis. Gastroenterol Hepatol Bed Bench. 2012 Spring; 5(2): 79-83.
In article      
 
[18]  Kahlert J, Gribsholt SB, Gammelager H, Dekkers OM, Luta G. Control of confounding in the analysis phase – an overview for clinicians. Clin Epidemiol. 2017; 9: 195-204.
In article      View Article  PubMed
 
[19]  Chander NG. Study validity. J Indian Prosthodont Soc. 2018; 18(1): 1-2.
In article      View Article  PubMed
 
[20]  Ain QU, Sarfraz M, Prasesti GK, Dewi TI, Kurniati NF. Confounders in Identification and Analysis of Inflammatory Biomarkers in Cardiovascular Diseases. Biomolecules. 2021; 11(10): 1464. Published 2021 Oct 5.
In article      View Article  PubMed
 
[21]  Rojanaworarit C, Claudio L, Howteerakul N, et al. Hydrogeogenic fluoride in groundwater and dental fluorosis in Thai agrarian communities: a prevalence survey and case-control study. BMC Oral Health. 2021; 21(1):545. Published 2021 Oct 22.
In article      View Article  PubMed
 
[22]  Ren X, Larsen SC, Lauritzen L, et al. Intake of n-3 LCPUFA and trans-fatty acids is unrelated to development in body mass index and body fat among children. BMC Nutr. 2022; 8(1): 1. Published 2022 Jan 3.
In article      View Article  PubMed
 
[23]  Reyes BD, Hargreaves DS, Creese H. Early-life maternal attachment and risky health behaviours in adolescence: findings from the United Kingdom Millennium Cohort Study. BMC Public Health. 2021; 21(1): 2039. Published 2021 Nov 8.
In article      View Article  PubMed
 
[24]  Wu, CC., Chu, YH., Shete, S. et al. Spatially varying effects of measured confounding variables on disease risk. Int J Health Geogr 20, 45 (2021).
In article      View Article  PubMed
 
[25]  Peteranderl S and Edelsbrunner PA (2020) The Predictive Value of Children's Understanding of Indeterminacy and Confounding for Later Mastery of the Control-of-Variables Strategy. Front. Psychol. 11:531565.
In article      View Article  PubMed
 
[26]  Cynthia Van Landingham, William G. Fuller & Rosalind A. Schoof. (2020). The effect of confounding variables in studies of lead exposure and IQ, Critical Reviews in Toxicology, 50: 9, 815-825.
In article      View Article  PubMed
 
[27]  Vujkovic-Cvijin, I., Sklar, J., Jiang, L. et al. Host variables confound gut microbiota studies of human disease. Nature 587, 448-454 (2020).
In article      View Article  PubMed
 
[28]  Rusticus S. (2014). Content Validity. In: Michalos A.C. (eds) Encyclopedia of Quality of Life and Well-Being Research. Springer, Dordrecht.
In article      View Article
 
[29]  Halek, M., Holle, D. & Bartholomeyczik, S. Development and evaluation of the content validity, practicability and feasibility of the Innovative dementia-oriented Assessment system for challenging behaviour in residents with dementia. BMC Health Serv Res 17, 554 (2017).
In article      View Article  PubMed
 
[30]  Criterion-related validity. https://www.sciencedirect.com/topics/nursing-and-health-professions/criterion-related-validity.
In article      
 
[31]  Ginty A.T. (2013) Construct Validity. In: Gellman M.D., Turner J.R. (eds) Encyclopedia of Behavioral Medicine. Springer, New York, NY.
In article      View Article
 
[32]  Turner DP. Sampling Methods in Research Design. Headache. 2020 Jan; 60(1): 8-12.
In article      View Article  PubMed
 
[33]  Berndt AE. Sampling Methods. J Hum Lact. 2020 May; 36(2): 224-226.
In article      View Article  PubMed
 
[34]  Guest G, Namey E, Chen M. A simple method to assess and report thematic saturation in qualitative research. PLoS One. 2020 May 5; 15(5): e0232076.
In article      View Article  PubMed
 
[35]  Tripathi R, Khatri N, Mamde A. Sample Size and Sampling Considerations in Published Clinical Research Articles. J Assoc Physicians India. 2020 Mar; 68(3): 14-18.
In article      
 
[36]  Gill SL. Qualitative Sampling Methods. J Hum Lact. 2020 Nov; 36(4): 579-581. Epub 2020 Aug 19. PMID: 32813616.
In article      View Article  PubMed
 
[37]  Understanding different sampling methods https://www.scribbr.com/methodology/sampling-methods/.
In article      
 

Published with license by Science and Education Publishing, Copyright © 2022 Venkataramana Kandi

Creative CommonsThis work is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

Cite this article:

Normal Style
Venkataramana Kandi. Research Process, Study Variables, Statistical Validations, and Sampling Methods in Public Health Related Research: An Update. American Journal of Biomedical Research. Vol. 10, No. 1, 2022, pp 1-8. http://pubs.sciepub.com/ajbr/10/1/1
MLA Style
Kandi, Venkataramana. "Research Process, Study Variables, Statistical Validations, and Sampling Methods in Public Health Related Research: An Update." American Journal of Biomedical Research 10.1 (2022): 1-8.
APA Style
Kandi, V. (2022). Research Process, Study Variables, Statistical Validations, and Sampling Methods in Public Health Related Research: An Update. American Journal of Biomedical Research, 10(1), 1-8.
Chicago Style
Kandi, Venkataramana. "Research Process, Study Variables, Statistical Validations, and Sampling Methods in Public Health Related Research: An Update." American Journal of Biomedical Research 10, no. 1 (2022): 1-8.
Share
[1]  Al-Riyami A. How to prepare a Research Proposal. Oman Med J. 2008; 23(2): 66-69.
In article      
 
[2]  Al-Shukaili A, Al-Maniri A. Writing a Research Proposal to The Research Council of Oman. Oman Med J. 2017; 32(3): 180-188.
In article      View Article  PubMed
 
[3]  Tullu MS. Writing the title and abstract for a research paper: Being concise, precise, and meticulous is the key. Saudi J Anaesth. 2019; 13(Suppl 1):S12-S17.
In article      View Article  PubMed
 
[4]  Bahadoran Z, Mirmiran P, Kashfi K, Ghasemi A. The Principles of Biomedical Scientific Writing: Title. Int J Endocrinol Metab. 2019; 17(4): e98326. Published 2019 Oct 22.
In article      View Article
 
[5]  Kumar A. Uneasy is the journey of publication that wears an inappropriate title. J Indian Soc Periodontol. 2021; 25(6): 459-460.
In article      View Article  PubMed
 
[6]  Forero DA, Lopez-Leon S, Perry G. A brief guide to the science and art of writing manuscripts in biomedicine. J Transl Med. 2020; 18(1): 425. Published 2020 Nov 10.
In article      View Article  PubMed
 
[7]  Zouaoui M. The Importance of Research Proposal https://www.univ-sba.dz/med_dialogue/images/Article.8/23.pdf.
In article      
 
[8]  Steps in Developing a Research Proposal https://courses.lumenlearning.com/ivytech-engl112/chapter/steps-in-developing-a-research-proposal/.
In article      
 
[9]  Sudheesh K, Duggappa DR, Nethra SS. How to write a research proposal?. Indian J Anaesth. 2016; 60(9): 631-634.
In article      View Article  PubMed
 
[10]  Confounding Variable: Simple Definition and Example https://www.statisticshowto.com/experimental-design/confounding-variable/.
In article      
 
[11]  Confounding variables http://www.biostathandbook.com/confounding.html.
In article      
 
[12]  Nominal, Ordinal, Interval & Ratio Variable + [Examples] https://www.formpl.us/blog/nominal-ordinal-interval-ratio-variable-example.
In article      
 
[13]  van Maaren, M.C., le Cessie, S., Strobbe, L.J.A. et al. Different statistical techniques dealing with confounding in observational research: measuring the effect of breast-conserving therapy and mastectomy on survival. J Cancer Res Clin Oncol 145, 1485-1493 (2019).
In article      View Article  PubMed
 
[14]  Groenwold RHH, Dekkers OM. METHODOLOGY FOR THE ENDOCRINOLOGIST: Basic aspects of confounding adjustment. Eur J Endocrinol. 2020 May; 182(5): E5-E7.
In article      View Article  PubMed
 
[15]  Lederer DJ, Bell SC, Branson RD, et al. Control of Confounding and Reporting of Results in Causal Inference Studies. Guidance for Authors from Editors of Respiratory, Sleep, and Critical Care Journals. Ann Am Thorac Soc. 2019 Jan; 16(1): 22-28.
In article      
 
[16]  Skelly AC, Dettori JR, Brodt ED. Assessing bias: the importance of considering confounding. Evid Based Spine Care J. 2012; 3(1): 9-12.
In article      View Article  PubMed
 
[17]  Pourhoseingholi MA, Baghestani AR, Vahedi M. How to control confounding effects by statistical analysis. Gastroenterol Hepatol Bed Bench. 2012 Spring; 5(2): 79-83.
In article      
 
[18]  Kahlert J, Gribsholt SB, Gammelager H, Dekkers OM, Luta G. Control of confounding in the analysis phase – an overview for clinicians. Clin Epidemiol. 2017; 9: 195-204.
In article      View Article  PubMed
 
[19]  Chander NG. Study validity. J Indian Prosthodont Soc. 2018; 18(1): 1-2.
In article      View Article  PubMed
 
[20]  Ain QU, Sarfraz M, Prasesti GK, Dewi TI, Kurniati NF. Confounders in Identification and Analysis of Inflammatory Biomarkers in Cardiovascular Diseases. Biomolecules. 2021; 11(10): 1464. Published 2021 Oct 5.
In article      View Article  PubMed
 
[21]  Rojanaworarit C, Claudio L, Howteerakul N, et al. Hydrogeogenic fluoride in groundwater and dental fluorosis in Thai agrarian communities: a prevalence survey and case-control study. BMC Oral Health. 2021; 21(1):545. Published 2021 Oct 22.
In article      View Article  PubMed
 
[22]  Ren X, Larsen SC, Lauritzen L, et al. Intake of n-3 LCPUFA and trans-fatty acids is unrelated to development in body mass index and body fat among children. BMC Nutr. 2022; 8(1): 1. Published 2022 Jan 3.
In article      View Article  PubMed
 
[23]  Reyes BD, Hargreaves DS, Creese H. Early-life maternal attachment and risky health behaviours in adolescence: findings from the United Kingdom Millennium Cohort Study. BMC Public Health. 2021; 21(1): 2039. Published 2021 Nov 8.
In article      View Article  PubMed
 
[24]  Wu, CC., Chu, YH., Shete, S. et al. Spatially varying effects of measured confounding variables on disease risk. Int J Health Geogr 20, 45 (2021).
In article      View Article  PubMed
 
[25]  Peteranderl S and Edelsbrunner PA (2020) The Predictive Value of Children's Understanding of Indeterminacy and Confounding for Later Mastery of the Control-of-Variables Strategy. Front. Psychol. 11:531565.
In article      View Article  PubMed
 
[26]  Cynthia Van Landingham, William G. Fuller & Rosalind A. Schoof. (2020). The effect of confounding variables in studies of lead exposure and IQ, Critical Reviews in Toxicology, 50: 9, 815-825.
In article      View Article  PubMed
 
[27]  Vujkovic-Cvijin, I., Sklar, J., Jiang, L. et al. Host variables confound gut microbiota studies of human disease. Nature 587, 448-454 (2020).
In article      View Article  PubMed
 
[28]  Rusticus S. (2014). Content Validity. In: Michalos A.C. (eds) Encyclopedia of Quality of Life and Well-Being Research. Springer, Dordrecht.
In article      View Article
 
[29]  Halek, M., Holle, D. & Bartholomeyczik, S. Development and evaluation of the content validity, practicability and feasibility of the Innovative dementia-oriented Assessment system for challenging behaviour in residents with dementia. BMC Health Serv Res 17, 554 (2017).
In article      View Article  PubMed
 
[30]  Criterion-related validity. https://www.sciencedirect.com/topics/nursing-and-health-professions/criterion-related-validity.
In article      
 
[31]  Ginty A.T. (2013) Construct Validity. In: Gellman M.D., Turner J.R. (eds) Encyclopedia of Behavioral Medicine. Springer, New York, NY.
In article      View Article
 
[32]  Turner DP. Sampling Methods in Research Design. Headache. 2020 Jan; 60(1): 8-12.
In article      View Article  PubMed
 
[33]  Berndt AE. Sampling Methods. J Hum Lact. 2020 May; 36(2): 224-226.
In article      View Article  PubMed
 
[34]  Guest G, Namey E, Chen M. A simple method to assess and report thematic saturation in qualitative research. PLoS One. 2020 May 5; 15(5): e0232076.
In article      View Article  PubMed
 
[35]  Tripathi R, Khatri N, Mamde A. Sample Size and Sampling Considerations in Published Clinical Research Articles. J Assoc Physicians India. 2020 Mar; 68(3): 14-18.
In article      
 
[36]  Gill SL. Qualitative Sampling Methods. J Hum Lact. 2020 Nov; 36(4): 579-581. Epub 2020 Aug 19. PMID: 32813616.
In article      View Article  PubMed
 
[37]  Understanding different sampling methods https://www.scribbr.com/methodology/sampling-methods/.
In article