16.2 Food and Nutrition Research Methods, Sampling, Sample Size, and Research Ethics

The research competency area of the Community and Public Health Nutrition table of specifications asks examinees to identify the scope and methods of food and nutrition research, prepare sampling techniques, and understand surveys. Study designs and risk measures are covered in the nutritional epidemiology section; this section focuses on the research process, sampling, statistics, and ethics.

Scope of Food and Nutrition Research

• Basic research: nutrient metabolism, food chemistry, and mechanisms of disease.
• Applied research: product development, food fortification, dietary interventions, and program effectiveness.
• Operations research: how to deliver programs better, such as improving supplementary feeding attendance.
• Social and behavioral research: food beliefs, feeding practices, and barriers to change.

The Research Process

1. Identify and state the problem.
2. Review related literature.
3. Formulate objectives and hypotheses.
4. Choose the research design.
5. Define the population and sampling method; compute the sample size.
6. Develop and pretest data collection tools.
7. Obtain ethical approval and informed consent.
8. Collect, encode, and clean data.
9. Analyze and interpret the data.
10. Write and disseminate the report.

Variables: the independent variable is the presumed cause or intervention (such as a nutrition education program); the dependent variable is the outcome (such as knowledge scores or hemoglobin). Confounding variables are related to both and can distort the association, such as household income.

Hypotheses: the null hypothesis states no difference or association; the alternative hypothesis states that a difference exists. A Type I error rejects a true null hypothesis (probability alpha, usually 0.05); a Type II error fails to reject a false null hypothesis (probability beta). Power (1 - beta, often 80%) is the chance of detecting a real effect.

Experimental and Qualitative Designs

Qualitative methods explain why and how, while quantitative methods measure how much and how many. Mixed methods combine both.

Sampling Techniques

Sample Size

Slovin's formula (commonly taught in the Philippines):

$$n = \frac{N}{1 + Ne^2}$$

For a barangay with N = 2,000 households and a 5% margin of error (e = 0.05):

$$n = \frac{2{,}000}{1 + 2{,}000(0.05)^2} = \frac{2{,}000}{6} = 333.3 \approx 334$$

For systematic sampling, the interval is k = 2,000 ÷ 334 ≈ 6, so the researcher picks a random start from 1 to 6 and then every sixth household.

Estimating a prevalence:

$$n = \frac{Z^2 p(1-p)}{d^2}$$

With an expected stunting prevalence p = 0.236, Z = 1.96 for 95% confidence, and precision d = 0.05:

$$n = \frac{(1.96)^2(0.236)(0.764)}{(0.05)^2} = \frac{0.6927}{0.0025} \approx 278$$

Cluster sampling usually needs a design effect multiplier, often about 2, which raises the sample to about 555 children. Researchers also add extra for expected non-response.

Validity, Reliability, and Bias

• Validity: the tool measures what it intends to measure (a validated FFQ compared against food records).
• Reliability: consistent results on repeated measurement (test-retest, inter-rater agreement).
• Selection bias: the sample differs systematically from the population.
• Information bias: errors in measurement, including recall bias.
• Confounding: a third factor explains the association; control it by randomization, matching, stratification, or statistical adjustment.
• Pretesting tools on a similar group reveals unclear questions before data collection.

Basic Statistics

A p-value below 0.05 is usually considered statistically significant.

Research Ethics

• Respect for persons: voluntary, informed consent; assent from children with parental permission.
• Beneficence and non-maleficence: maximize benefits and minimize harm.
• Justice: fair selection of participants and sharing of benefits.
• Confidentiality: the Data Privacy Act of 2012 (RA 10173) protects personal information.
• Ethical review: the Philippine National Health Research System Act of 2013 (RA 10532) supports ethics review through the Philippine Health Research Ethics Board (PHREB), which accredits research ethics committees and issues the National Ethical Guidelines for Research Involving Human Participants.