Randomized Controlled trials and Cohort studies

randomized Controlled trials and cohort studies

arantxa amaro, dds

PGY-1 Pediatric Dentistry

levels of evidence

Question type

Randomized controlled Trials (RCT)

Prospective clinical studies conducted to assess the effectiveness of a new intervention or treatment.

Participants are randomly allocated to either an experimental group receiving the intervention or a control group receiving standard care or a placebo.

The only expected difference between the control and experimental groups is the outcome variable being studied.

Zabor, E. C., Kaizer, A. M., & Hobbs, B. P. (2020). Randomized controlled trials. Chest, 158(1, Suppl), S79–S87. https://doi.org/10.1016/j.chest.2020.03.013Hariton E, Locascio JJ. Randomised controlled trials - the gold standard for effectiveness research: Study design: randomised controlled trials. BJOG. 2018

core features of RCT

Randomization

(receiving the treatment or exposure being studied) or the control group (receiving a placebo or standard treatment).

Blinding

It's used tto reduce bias.

outcome measurment

the outcomes are measured in both groups and compared to determine the effect of the intervention

Control group

the baseline for comparison

follow-up

Participants are followed over time to observe the outcomes and detect any differences between the groups

Zabor, E. C., Kaizer, A. M., & Hobbs, B. P. (2020). Randomized controlled trials. Chest, 158(1), S79-S87. https://doi.org/10.1016/j.chest.2020.03.013 Schulz, K. F., Altman, D. G., & Moher, D. (2010). CONSORT 2010 statement: updated guidelines for reporting parallel group randomized trials. Annals of Internal Medicine, 152(11), 726-732.

RCT - desing

PICO = "What’s the question?"

Comparison

Patient/Population/ Problem

Outcome

Intervention

FINER = "Should we ask it?"

relevant

novel

feasible

ethical

Intersting

O'Sullivan, D., Wilk, S., Michalowski, W., & Farion, K. (2013). Evidence-based medicine: A FINER PICO analysis. Studies in Health Technology and Informatics, 192, 1057–1061. https://doi.org/10.3233/978-1-61499-289-9-1057.

RCT STRENGTHS AND WEAKNESSES

Sibinga, E. M. S., & Jennings, J. M. (2010). Strengths and limitations of randomized, controlled trials. Pediatrics in Review, 31(7), 296–297.

Sample size An inadequate sample size can increase error and reduce the study's power Double Blinding A way to reduce bias by making it difficult to detect the intervention Randomization It is a strength of RCTs The randomization process should be kept hidden from both the participants and the people administering the intervention.

CONSIDERATIONS

AAPD RCT journal example

Wang, Z., Rong, W., & Xu, T. (2021). Effect of fluoride varnish in caries prevention on permanent first molars: A 36-month cluster randomized controlled trial. Pediatric Dentistry, 43(2), 82-87.

cohort studies

Observational study that follows a defined group (cohort) over time.

Compares incidence of an outcome in exposed vs. unexposed individuals.

Cohort studies are a type of longitudinal study, which means the participants are followed for an extended period of time.

Osmosis. (n.d.). Study design. Osmosis. Retrieved October 15, 2025, from https://www.osmosis.org/notes/Study_Design

prospective cohort study

• Researchers start with a group of individuals who do not have
• the outcome of interest and follow them forward in time to observe the exposure and outcome.

Osmosis. (n.d.). Study design. Osmosis. Retrieved October 15, 2025, from https://www.osmosis.org/notes/Study_Design

retrospective cohort study

Researchers look back at data from a group of people whowere exposed to a certain riskfactor and assess the outcome, using pre-existing records or data.

Osmosis. (n.d.). Study design. Osmosis. Retrieved October 15, 2025, from https://www.osmosis.org/notes/Study_Design

core features of cohort studies

timefrane

Exposure and Outcome

Involve tracking participants over time, which helps establish the relationship between exposure and outcome.

compare those exposed to a certain risk factor with those not exposed to see if there is a difference in outcomes.

association

Provide strong association between risk factors and outcomes

Mann, C. J. (2003). Observational research methods. Research design II: Cohort, cross sectional, and case-control studies. Emergency Medicine Journal, 20(1), 54–60. https://doi.org/10.1136/emj.20.1.54 Rothman, K. J., Greenland, S., & Lash, T. L. (2008). Modern epidemiology (3rd ed.). Lippincott Williams & Wilkins.2.

von Elm, E., Altman, D. G., Egger, M., Pocock, S. J., Gøtzsche, P. C., & Vandenbroucke, J. P. (2007). The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement: guidelines for reporting observational studies. EQUATOR Network. https://www.equator-network.org/reporting-guidelines/strobe/

AAPD cohort journal example

Edelstein, B. L., Ureles, S. D., & Smaldone, A. (2016). Very high salivary Streptococcus mutans predicts caries progression in young children. Pediatric Dentistry, 38(4), 325–330

Confounding factors: it is a variable that influences both the exposure and the outcome, potentially distorting the true relationship between them. •Positive confounding: Makes the association appear stronger. •Negative confounding: Makes the association appear weaker. Randomization: Participants are randomly assigned to exposure groups to equally distribute confounders.

CONSIDERATIONS

cohort STRENGTHS AND WEAKNESSES

Mann, C. J. (2003). Observational research methods. Research design II: Cohort, cross sectional, and case-control studies. Emergency Medicine Journal, 20(1), 54–60. https://doi.org/10.1136/emj.20.1.54 Rothman, K. J., Greenland, S., & Lash, T. L. (2008). Modern epidemiology (3rd ed.). Lippincott Williams & Wilkins Szklo, M., & Nieto, F. J. (2019). Epidemiology: Beyond the basics (4th ed.). Jones & Bartlett Learning. von Elm, E., Altman, D. G., Egger, M., Pocock, S. J., Gøtzsche, P. C., & Vandenbroucke, J. P. (2007). The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: Guidelines for reporting observational studies. Lancet, 370(9596), 1453–1457. https://doi.org/10.1016/S0140-6736(07)61602-X

RCT vs cohort

Mann, C. J. (2003). Observational research methods. Research design II: Cohort, cross sectional, and case-control studies. Emergency Medicine Journal, 20(1), 54–60. https://doi.org/10.1136/emj.20.1.54 Rothman, K. J., Greenland, S., & Lash, T. L. (2008). Modern epidemiology (3rd ed.). Lippincott Williams & Wilkins Szklo, M., & Nieto, F. J. (2019). Epidemiology: Beyond the basics (4th ed.). Jones & Bartlett Learning. von Elm, E., Altman, D. G., Egger, M., Pocock, S. J., Gøtzsche, P. C., & Vandenbroucke, J. P. (2007). The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: Guidelines for reporting observational studies. Lancet, 370(9596), 1453–1457. https://doi.org/10.1016/S0140-6736(07)61602-X

Thank you so much!

• Defined before the study begins (primary and secondary outcomes
• Objective and standardized measures increase validity
• Compared between groups to evaluate treatment effect

In pediatric dentistry, any differences in outcomes—such as oral health improvements or behavioral changes—are attributed to the intervention being studied, assuming all other variables are balanced through randomization.

Exposure/Outcome: Children classified by high vs. low salivary S. mutans levels. Timeframe: Prospective follow-up for more than 5 years. Association: Demonstrated a strong association between high S. mutans levels and future caries progression.

Shows cause and effect clearly – Random assignment makes it easier to know if the treatment really caused the outcome. Expensive and time-consuming – RCTs often need a lot of money, staff, and time to complete. Reduces bias – Randomization helps make the groups similar, so results are fair. Not always practical or ethical – Sometimes it’s not possible to randomly assign people (e.g., to harmful exposures). High reliability – Well-designed RCTs produce trustworthy results that are less likely to be influenced by outside factors. Dropouts can affect results – If many people leave the study, it can reduce the quality of the data. Clear comparison between groups – Makes it easy to measure differences in outcomes between treatment and control groups.

The investigator: Select the cohort based on: Exposure to a particular risk factor Observe: the development a certain outcome, such as a disease

• Participants monitored for a predetermined period
• Tracks changes in health status or behavior
• Helps identify both benefits and adverse effects

Expensive and time-consuming – RCTs often need a lot of money, staff, and time to complete. Not always practical or ethical – Sometimes it’s not possible to randomly assign people (e.g., to harmful exposures). Dropouts can affect results – If many people leave the study, it can reduce the quality of the data.

• Can receive a placebo, standard treatment, or no intervention
• Essential for understanding if the intervention is truly effective
• Acts as a benchmark for comparison

• Randomly assigns participants to groups to avoid selection bias

• Ensures groups are comparable in characteristics

• Types: Simple, block, stratified randomization

Time-consuming and expensive (especially prospective designs). Inefficient for rare diseases (large sample sizes needed). Loss to follow-up may introduce attrition bias. Exposure misclassification or changes in exposure status over time can bias results. Vulnerable to confounding variables (e.g., socioeconomic status, diet, genetics).

Establishes temporal relationship (exposure before outcome). Can calculate incidence rates and relative risk (RR) directly. Allows study of multiple outcomes for a single exposure. Useful for studying rare exposures (e.g., environmental fluoride exposure, specific medications). Less prone to recall bias (exposures measured before outcomes).

• Single-blind: Participants unaware of group assignment
• Double-blind: Both participants and researchers unaware
• Purpose: Prevents bias in treatment administration and outcome assessment

STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines ▪ Created to aid the author in ensuring high-quality presentation of the conducted observational study ▪ 22 checklist items ▪ The authors complying with these guidelines are more likely to succeed in publishing their study.

Population (P): 6–7-year-old children with newly erupted permanent first molars Intervention (I): 5% sodium fluoride varnish applied twice yearly Comparison (C): No varnish (control group) Outcome (O): Caries incidence on permanent first molars over 36 months

Follow-up from birth to age 3 assessing professional fluoride applications and dental visits.

Primary Research

Purpose: To answer a specific research question by collecting new data. Each study stands on its own and offers a single piece of evidence. In Pediatric Dentistry: A study measuring the effectiveness of silver diamine fluoride (SDF) in preventing caries in children

COBWEB (CONSORT-BASED WEB) is an online manuscript writing aid tool intended to guide authors through the process of manuscript writing of Randomized Controlled Trials (RCTs) in line with the Consolidated Standards of Reporting Trials (CONSORT) and its subsequent extensions.

• Single-blind: Participants unaware of group assignment
• Double-blind: Both participants and researchers unaware
• Purpose: Prevents bias in treatment administration and outcome assessment

• Can receive a placebo, standard treatment, or no intervention
• Essential for understanding if the intervention is truly effective
• Acts as a benchmark for comparison

Example: Fluoride exposure in drinking water and risk of dental caries.

High levels of salivary Streptococcus mutans predict caries progression over several years.

Synthesized Research

Purpose: To gather, evaluate, and summarize all available high-quality evidence on a question, reducing the risk of bias by aggregating findings from many studies. In Pediatric Dentistry: A systematic review comparing multiple RCTs on fluoride varnish in preventing early childhood