Table A1.

STROBE Statement – Checklist of Items that Should Be Included in Reports of Observational Studies

	Item No	Recommendation
Title and abstract	1	(a) Indicate the study’s design with a commonly used term in the title or the abstract The data used for the demonstration of the methodology is from a cohort study. The Iowa Fluoride Study (IFS) recruited a birth cohort at eight Iowa hospitals. The IFS followed this cohort, collecting regular dietary and beverage intakes as well as completing dental examinations at about ages 5, 9, 13, and 17 (b) Provide in the abstract an informative and balanced summary of what was done and what was found This has been completed.
Introduction
Background/rationale	2	Explain the scientific background and rationale for the investigation being reported We explain that statistical modeling is evolving and that modeling approaches beyond P-values need to be understood and adopted (pages 4–5).
Objectives	3	State specific objectives, including any prespecified hypotheses The objective is to demonstrate the use of a statistical method in the context of a dental study. There are no prespecified hypotheses.
Methods
Study design	4	Present key elements of study design early in the paper NA – This project does not focus on the Iowa Flouride Study, but rather it describes a methodology that can be used in the modeling of the data from the study.
Setting	5	Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection NA – This project does not focus on the Iowa Flouride Study, but rather it describes a methodology that can be used in the modeling of the data from the study.
Participants	6	(a) Cohort study – Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of follow-up Case-control study – Give the eligibility criteria, and the sources and methods of case ascertainment and control selection. Give the rationale for the choice of cases and controls Cross-sectional study – Give the eligibility criteria, and the sources and methods of selection of participants NA – This project does not focus on the Iowa Flouride Study, but rather it describes a methodology that can be used in the modeling of the data from the study. (b) Cohort study – For matched studies, give matching criteria and number of exposed and unexposed Case-control study – For matched studies, give matching criteria and the number of controls per case NA – This project does not focus on the Iowa Flouride Study, but rather it describes a methodology that can be used in the modeling of the data from the study.
Variables	7	Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if applicable The outcome is described in the “Outcome Variable” section under “Methods.” The candidate predictors are described in the “Candidate Predictor Variables” section under “Methods.”
Data sources/measurement	8*	For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe comparability of assessment methods if there is more than one group The source and details of methods assessment for the outcome data (dental examinations) are described in the “Outcome Variable” section under “Methods.” The source and details of methods assessment for the predictor variables are described in the “Candidate Predictor Variables” section under “Methods.”
Bias	9	Describe any efforts to address potential sources of bias NA – This project does not focus on the Iowa Flouride Study, but rather it describes a methodology that can be used in the modeling of the data from the study
Study size	10	Explain how the study size was arrived at NA – This project does not focus on the Iowa Flouride Study, but rather it describes a methodology that can be used in the modeling of the data from the study.
Quantitative variables	11	Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and why Three different representation methods are considered for the longitudinal dietary variables of interest. Since this paper serves as a demonstration of a methodology, we felt three representation methods were sufficient for illustrative purposes.
Statistical methods	12	(a) Describe all statistical methods, including those used to control for confounding We did not control for confounding in this analysis. The purpose was to introduce a methodological approach. The statistical method is described in the “Akaike Information Criterion (AIC)” section under “Methods.” (b) Describe any methods used to examine subgroups and interactions Subgroups and interactions are not considered. (c) Explain how missing data were addressed We averaged over time points which will allow for missing observations. This is described in the “Candidate Predictor Variables” section under Methods. Missing averages were removed prior to the analyses in order to use the presented methodology. (d) Cohort study – If applicable, explain how loss to follow-up was addressed Case-control study – If applicable, explain how matching of cases and controls was addressed Cross-sectional study – If applicable, describe analytical methods taking account of sampling strategy NA (e) Describe any sensitivity analyses NA – In a different manuscript where we use this methodology, such an analysis is presented.
Results
Participants	13*	(a) Report numbers of individuals at each stage of study – for example, numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing follow-up, and analyzed This is described in the “Iowa Fluoride Study Background” section under “Methods.” There were 396 participants with data, but only 344 participants were used in the final analysis due to missingness. (b) Give reasons for nonparticipation at each stage NA – This project does not focus on the Iowa Flouride Study, but rather it describes a methodology that can be used in the modeling of the data from the study. (c) Consider use of a flow diagram NA – This project does not focus on the Iowa Flouride Study, but rather it describes a methodology that can be used in the modeling of the data from the study.
Descriptive data	14*	(a) Give characteristics of study participants (e.g., demographic, clinical, social) and information on exposures and potential confounders NA – This project does not focus on the Iowa Flouride Study, but rather it describes a methodology that can be used in the modeling of the data from the study. (b) Indicate number of participants with missing data for each variable of interest This is described in the “Iowa Fluoride Study Background” section under “Methods.” (c) Cohort study – Summarise follow-up time (e.g., average and total amount) NA – This project does not focus on the Iowa Flouride Study, but rather it describes a methodology that can be used in the modeling of the data from the study.
Outcome data	15*	Cohort study – Report numbers of outcome events or summary measures over time This is described in the “Outcome Variable” section under “Methods.” There were 344 participants who were categorized into three different caries trajectories groups. Case-control study – Report numbers in each exposure category, or summary measures of exposure Cross-sectional study – Report numbers of outcome events or summary measures
Main results	16	(a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (e.g., 95% confidence interval). Make clear which confounders were adjusted for and why they were included NA – The presented methodology does not focus on the unadjusted estimates, but rather focuses on variable selection through penalized fit. (b) Report category boundaries when continuous variables were categorized NA – Continuous predictor variables were not categorized. (c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period NA
Other analyses	17	Report other analyses done – for example, analyses of subgroups and interactions, and sensitivity analyses The modeling methodology is employed in another manuscript that focuses on analyses, results, and conclusions as opposed to the presentation of a methodological approach. Sensitivity and other analyses are not applicable here.
Discussion
Key results	18	Summarise key results with reference to study objectives This is described in the “Discussion” section.
Limitations	19	Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude of any potential bias Limitations are discussed in a paragraph in the “Discussion” section.
Interpretation	20	Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence This is described in the “Discussion” section.
Generalisability	21	Discuss the generalizability (external validity) of the study results This is covered in the both the “Introduction” and “Discussion” sections. The methodology presented here can be applied to many statistical modeling frameworks.
Other information
Funding	22	Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the present article is based This information is included in a “Funding” passage at the end of the manuscript.

^*Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies.

Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at http://www.annals.org/, and Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.