The study sample is the enumerated set of individuals whose information is captured in a data set, among whom we attempt to measure occurrence of the outcome (after inclusion and exclusion criteria have been applied, if data were not collected using these criteria (e.g., administrative data)). For valid inferences, the incidence of the outcome in the sample must be able to stand in for the incidence in the target population. Among those initiating at ages 910, 93% of 13-year-olds completed the series. Additionally, 4) any auxiliary variables will be prespecified and their roles as stratification factors (to characterize the outcome distribution) or nuisance variables (to be standardized over) will be stated. Example: The surveillance data include everyone in the target population (age 18 years, alive, diagnosed with HIV, and 1 HIV care visit before December 31, 2019), but they also include some people who are not in the target population (they include people who did not make 1 HIV care visit with a clinician who might prescribe antiretroviral medications), and we are unable to definitively identify people in the surveillance data who do not meet the inclusion criteria for the target population (we have to rely on laboratory tests as a proxy for clinical visits) (19). There are many personal characteristics and behaviors that are relevant to health status and might be considered "exposures" or risk factors that ought to be considered when conducting research on the determinants of disease or when trying to predict risk. Lesko CR, Buchanan AL, Westreich D, et al. Reasons for gender differences in mortality may include: There is mandated reporting in the United States of new HIV diagnoses and HIV viral load test results to public health surveillance agencies under national notifiable disease regulations, and the Centers for Disease Control and Prevention aggregates these data from all states and dependent areas. Med 96:875, 1982]. No potential conflict of interest was reported by the author(s). Example 1: Stomach Cancer by Location in the US. Any survey respondents with provider-verified HPV vaccine receipt either younger than 9years of age or at 18years were excluded from analysis. C. Allows comparisons by age, sex, and race. A well-defined descriptive question aims to quantify and characterize some feature of the health of a population and must clearly state: 1) the target population, characterized by In this paper, we propose a framework for thinking through the design and conduct of descriptive epidemiologic studies. One interesting finding from this analysis was that for the adolescents who initiated HPV vaccination at 910years of age, series up-to-date status rates were consistently greater than 93%, with little difference by age or sex. Wayne W. LaMorte, MD, PhD, MPH, Boston University School of Public Health, Characteristics of Person, Place, and Time, Person: Personal Characteristics and Behaviors, Other Factors That Can Produce Changes in Disease Frequency Over Years or Decades, https://archive.org/details/atlasofcancermor00nati_0, Religious practices, e.g. -the occurrence of chronic disease. Measurement error has previously been described as a missing-data problem (22) in which the true outcome is missing and we overwrite that missing value with a mismeasured outcome. The maps below show death rates from stomach cancer in females and males in different US counties. Again, the National U.S. Census still uses the category sex to report, male, or, female; but is essentially incorrect. Kong WY, Huang Q, Thompson P, Grabert BK, Brewer NT, Gilkey MB. Age at initiation of human papillomavirus vaccination among US adolescents, stratified by key sociodemographic characteristics, national immunization survey-2020. NIS-Teen data have been collected by the CDC to monitor vaccination coverage of Tdap, MCV4, and HPV among 1317-year-old adolescents in the US since 2006. Descriptive epidemiology classifies the occurrence of disease according to the variables of person, place, and time. Inclusion in an NLM database does not imply endorsement of, or agreement with, Respond to The Importance of Descriptive Epidemiology' and 'Invited Commentary: The Importance of Descriptive Epidemiology' (doi: 10.1093/aje/kwac152, 10.1093/aje/kwac153). The figure below shows the usual cycle of . However, some of the other continuous variables do differ across the exposure groups, e.g., body mass index, alcohol consumption, and dietary cholesterol. First, notice that for certain variables, the values are numeric; for others, the values are descriptive. When characterizing groups with the highest incidence of the outcome, bivariate results can make it challenging to understand how covariates interact to determine the distribution of disease. Additionally, not everyone in either of our candidate study samples will have had a viral load measurement on December 31, 2019, exactly. We illustrate application of this framework to describe the prevalence of viral suppression on December 31, 2019, among people living with human immunodeficiency virus (HIV) who had been linked to HIV care in the United States. As part of this analysis, we compared the frequency of being up-to-date (UTD) for HPV vaccination based on age at first vaccine dose, and compared vaccine uptake epidemiology across multiple socio-demographic measures. Could the high rates of stomach cancer be the result of their consumption of smoked fish or other traditional methods of food preservation? First, the data analyzed come from the NIS-Teen, which is subject to potential selection bias due to the use of random digit dialing, and incomplete assessment of all adolescents vaccine history by their providers. Describe any assumptions or methods used to extrapolate data from the analytical sample to the study population and from the study population to the target population. Prevalent outcomes are often not of interest in causal investigations, as temporality is more challenging to determine and reverse causation is a potential problem. The probability of viral suppression among these individuals is near 0 (we might think of loss to follow-up as a competing event and assign a value of not suppressed to persons who are lost to follow-up) (42). Elvstam O, Medstrand P, Yilmaz A, et al. Created by mackinzie_goeke Terms in this set (26) True or False? Risk is arguably the most easily interpretable measure of disease occurrence for the general public (33). Lesko CR, Sampson LA, Miller WC, et al. Reagan-Steiner S, Yankey D, Jeyarajah J, Elam-Evans LD, Singleton JA, Curtis CR, MacNeil J, Markowitz LE, Stokley S. National, regional, state, and selected local area vaccination coverage among adolescents aged 1317 years United States, 2014. However, the resultant risks are interpretable as the risk that would have been observed if no one were lost to follow-up (a hypothetical intervention), and will be different from the natural course if loss to follow-up was associated with the outcome in ways not captured by covariates in the weight model or if loss to follow-up itself directly altered the risk of the outcome (18, 40). 2. Items That Should Be Included in Reports of Descriptive Studies. a. Homicides and suicides Application of this framework highlights biases that may arise from missing data, especially 1) differences between the target population and the analytical sample; 2) measurement error; 3) competing events, late entries, loss to follow-up, and inappropriate interpretation of the chosen measure of outcome occurrence; and 4) inappropriate adjustment. This study has some limitations. Typically, researchers accept viral loads measured within a time window around some key date as indicative of the viral load on that key date. Preventing tetanus, diphtheria, and pertussis among adolescents: use of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccines recommendations of the Advisory Committee on Immunization Practices (ACIP), Prevention and control of meningococcal disease. Introduction Field investigations are usually conducted to identify the factors that increased a person's risk for a disease or other health outcome. Performing rigorous descriptive studies that accurately estimate a parameter of interest and are interpretable to clinicians and policy-makers will improve public health. Risk (the proportion of people free from disease at baseline who develop the outcome during the study period) is the foundation of many causal epidemiologic studies (33), particularly as the target trial framework (1) has gained in popularity. The https:// ensures that you are connecting to the 1. Robert E. Fontaine Organizing Epidemiologic Data Characterizing The Cases (What?) We conducted all analyses using the 2020 NIS-Teen public use datafile.14 All analyses were done using SAS v9.4 (The SAS Institute, Cary NC). Time (When?) Is this due to a genetic difference? Note that each stage is more extensive than the previous one and generally carries a less favorable prognosis, but you cannot say that the difference between Stages 1 and 3 is the same as the difference between Stages 2 and 4. While the effect of this on coverage estimates leads only to minor differences, it is important to point out that our analysis specifically focused on vaccination related to specific timepoints in the HPV vaccine recommendations. Second, our coverage estimates may not fully align with the published NIS-Teen estimates, as we dropped any records from analysis where the age at first HPV vaccine dose was less than 9 or greater than 17years. Age cohorts maximized HPV vaccine completion after 34years. The conditional risk is the proportion of people free from disease at baseline that we would expect to develop the outcome during the study period if all competing events were prevented without changing the hazard of the event of interest; it is the risk conditional on removal of the competing event. Measures of occurrence. A well-defined question specifies the target population a priori. Perhaps in an idealized descriptive study, we would report the daily risk of HIV diagnosis restricted to people who were alive and at risk for HIV diagnosis at the start of each day. We start with the premise that good epidemiologic questions are impactful and well-defined. Explicitly state that this is a descriptive study in the title or the abstract. North American AIDS Cohort Collaboration on Research and Design. Uptake of human papillomavirus, tetanus/diphtheria/acellular pertussis, and quadrivalent meningococcal conjugate vaccine, stratified by key sociodemographic characteristics, 2020 national immunization survey-teen. While up-to-date status rates for initiators older than 910years are lower, they do consistently increase with increasing adolescent age. Therefore, we might use surveillance data for our primary analyses, but we might conduct secondary analyses that leverage the relative strengths of the different study samples and, for example, reweight NA-ACCORD data that include visits to resemble the target population implied by the surveillance data. St Sauver JL, Rutten LJF, Ebbert JO, Jacobson DJ, McGree ME, Jacobson RM. Look again at the variables (columns) and values (individual entries in each column) in Table 2.1. Previous analyses of HPV vaccine series initiation with regard to race, ethnicity, and poverty status have highlighted that traditional health disparities in terms of vaccine uptake are reversed for HPV vaccination. Research reported in this publication was supported by the American Lebanese and Syrian Associated Charities (ALSAC) of St. Jude Childrens Research Hospital and by grant 1R37CA234119 from the National Cancer Institute (NCI). One strategy to improve HPV vaccination is starting the vaccine series at the first opportunity currently as young as 9years of age. Different measures of occurrence will provide different pictures of what is happening in the world. Alternatively, we may want to account for nuisance variables, such as factors that differ between the study sample and the target population or between groups we plan to stratify by. In the presence of competing events, we have the option to report the conditional or unconditional risk (i.e., cumulative incidence function) (35). Or state to state? the contents by NLM or the National Institutes of Health. Parent and provider perspectives on immunization: are providers overestimating parental concerns? When looking at age as a continuous variable, standard epidemiological textbooks such as Rothman and Greenland's and many others recommend registering age as precisely as . For descriptive questions, consideration of additional variables is optional, but if auxiliary variables will be considered, a well-defined descriptive question will 4) prespecify any other variables of interest and how they will be considered (e.g., to characterize the population, as a stratification factor to characterize the outcome distribution, or as a nuisance variable that we would like to adjust for or standardize over). We define a descriptive epidemiologic question as one that aims to quantify some feature of the health of a population and, often, to characterize the distribution of that feature across the population. Perkins RB, Legler A, Jansen E, Bernstein J, Pierre-Joseph N, Eun TJ, Biancarelli DL, Schuch TJ, Leschly K, Fenton ATHR, et al. There were also dramatic changes in the frequency of the Ebola epidemic in Africa in 2017, as shown below. There are several frameworks intended to help guide causal analyses (1, 2), but the literature on theoretical and practical guidance for conducting descriptive analyses is limited. For our example question, the target population is everyone living in the United States (place) who was aged18 years, was infected and diagnosed with HIV, and attended 1 clinical visit for HIV care with a clinician who was aware of their infection and could prescribe antiretroviral medication (person) before December 31, 2019, and was alive through December 31, 2019 (time). Autism: This slide shows the increase in the number of children diagnosed with Autism from 1992 to 2006. National, regional, state, and selected local area vaccination coverage among adolescents aged 1317 years United States, 2015. Epidemiologic questions arguably exist on a continuum from purely descriptive to purely causal. For example, the tuberculin skin tests of a group of persons potentially exposed to a co-worker with tuberculosis can be measured as positive or negative (nominal scale) or in millimeters of induration (ratio scale). However, one should think broadly about the many other personal characteristics that might be important, such as: Where one lives, works, and travels can provide clues about relevant exposures. If our goal is to describe the world as it exists, absent hypothetical interventions, the cumulative incidence function is recommended when the number of competing events is nontrivial (37). While the proportion of adolescents initiating HPV vaccination at 910years was relatively low, series up-to-date status among these adolescents was consistently high (ranging from 93% to 100% across age- and sex-groups). The descriptive epidemiologic variable AGE is related to: b. Mortality from unintentional injuries, d. congenital malformations and infectious disease incidence in childhood. To gain a fuller picture of adolescent vaccination, our primary outcomes were receipt of at least one dose of HPV vaccine and being UTD for the HPV vaccine series; additionally, we included measures for vaccination with at least one dose of Tdap and MCV4 vaccines. Changes in incidence due to environmental or life-style changes. This research details where health events take place. Hypotheses about the determinants of disease arise from considering the characteristics of person, place, and time and looking for differences, similarities, and correlations. The graph shows that prior to 1978 there were just occasional cases of toxic shock syndrome in the United States. This provided a key clue suggesting a link to certain brands of tampons. (a) Avoid causal interpretations of descriptive results; avoid overinterpreting stratum-specific differences in measures of occurrence. Oxford University Press is a department of the University of Oxford. Saving Lives, Protecting People, Principles of Epidemiology in Public Health Practice, Third Edition, National Center for State, Tribal, Local, and Territorial Public Health Infrastructure and Workforce, U.S. Department of Health & Human Services, ____ Highest alanine aminotransferase (ALT). (a) Present an overall (unstratified) estimate of the measure of occurrence of interest. A CDC task force investigated and eventually traced the outbreak to the introduction of Rely tampons, a super absorbent product marketed by Proctor and Gamble. Walker TY, Elam-Evans LD, Singleton JA, Yankey D, Markowitz LE, Fredua B, Williams CL, Meyer SA, Stokley S. National, regional, state, and selected local area vaccination coverage among adolescents aged 1317 years United States, 2016. Note that rates of stomach cancer tend to be high in counties in the north-central part of the country in both males and females. Elam-Evans LD, Yankey D, Singleton JA, Sterrett N, Markowitz LE, Williams CL, Fredua B, McNamara L, Stokley S. National, regional, state, and selected local area vaccination coverage among adolescents aged 1317 Years United States, 2019. This lack of birth date data makes combining multiple years of NIS-Teen data together, with a focus on adolescent age, difficult, as small differences in timing of surveys and survey year could lead to misclassification. Another benefit of rates is that they are straightforward to estimate when we do not have individual-level data, which is more common in descriptive analyses than in causal or predictive epidemiologic analyses. Table 3 presents age at HPV vaccine series initiation and proportion of series initiators who completed the series, stratified by adolescent age and sex. The ideal data set for answering our descriptive epidemiologic question includes a row for everyone in the target population and columns with values for the outcome and any covariates of interest. Types of Descriptive Epidemiology Studies: Case Reports, Case Series, Cross-Sectional. The epidemiologist generally handles age in two ways: as a continuous variable, or as a categorised variable by combining a number of adjacent ages into a joint category. Could consumption of large amounts of smoked fish be a cause of stomach cancer? When we would like to describe incidence across a time metric along which not all people were biologically at risk at the time origin, rates can appropriately exclude person-time not at risk and allow for reporting of smoothed incidence estimates. Lower thresholds will result in a lower estimate of the prevalence of viral suppression; for example, in an HIV clinical cohort in Baltimore, Maryland, the proportion of patients estimated to have a suppressed viral load in a given year from 2010 to 2018 was 75% if the threshold for suppression was set at <20 copies/mL but 89% if the threshold was set at <400 copies/mL (24). Centers for Disease Control and Prevention . Improvements in diagnosis may increase cases reported even though the incidence may not be changing. Lee KK, Fitts MS, Conigrave JH, et al. While we were able to classify adolescents by age, we did not have specific birth date data to identify birth cohorts. Child and adolescent immunization schedule. The Author(s) 2022. You will be subject to the destination website's privacy policy when you follow the link. False Large international variations in rates of infectious and communicable diseases as well as other conditions are most likely explained by These two components work together to increase our understanding of the health population. The estimation challenge for descriptive analyses is that we may not completely observe all of the actual outcomes. Descriptive epidemiology covers time, place, and person. Among those initiating at 1112, completion rates rose from 66% among 13-year-olds to 90.2% among 16-year-olds. Changes in the age distribution of a population can produce changes in the overall rate of disease, even if age-specific rates are not changing. To account for socio-demographic characteristics, we used available covariate data on adolescents sex, age, history of 1112year old well visit, poverty status (recoded to at/above poverty and below poverty), race, and Hispanic ethnicity. e. all of the above. We might even choose to estimate the parameter of interest in multiple samples and triangulate the results. If, instead, it is plausible to assume that data are missing at random conditional on covariates that are available for target population members who were not selected for the study sample, we could reweight or standardize the study sample to represent the full target population. Descriptive epidemiology focuses on identifying and reporting both the pattern and frequency of health events in a population analytic epidemiology focuses on the search for the determinants of health outcomes. Changes in record keeping (accuracy) can create what appear to be changes in disease rates. The cumulative incidence function (or, as is implied but is a less commonly used term, the unconditional risk) is the proportion of people free from disease at baseline who would develop the outcome of interest during the study period in the real world in which a competing event might remove them from follow-up and preclude them from ever developing the outcome of interest. 2003-2023 Chegg Inc. All rights reserved. Elam-Evans LD, Yankey D, Jeyarajah J, Singleton JA, Curtis RC, MacNeil J, Hariri S. National, regional, state, and selected local area vaccination coverage among adolescents aged 13-17 years--United States, 2013. More recent birth cohorts had slightly higher initiation proportions than later birth cohorts adolescents (5% for 13 and 14year olds, compared to 3% for 16 and 17year olds). Overall adolescent vaccine coverage related to the 2020 NIS-Teen has been previously reported.15 The epidemic curves for Guinea, Liberia, and Sierra Leone show that the number of Ebola cases began to rise in March 2014, peaked in mid 2015, and then gradually fell by January 2016. National, regional, state, and selected local area vaccination coverage among adolescents aged 1317 years United States, 2020, A users guide for the 2020 public-use data file. However, parents report a willingness to have adolescents vaccinated against HPV starting at the first opportunity, as this may result in fewer vaccines given at well-care visits,12 as well as a lower level of concern about sexual activity by parents.13. (a) State when and how the outcome is measured. The field ofdescriptive epidemiologyclassifies the oc- currence of disease according to the variables of person (who is affected), place (where the condition occurs), and time (when and over what time period the condition has oc- curred). However, the NIS-Teen methods are robust and have been used for nearly two decades, and provide a solid framework for assessing adolescent vaccination in the US. Adolescents living below the poverty line were approximately 2.5 times more likely to initiate at 910years of age compared to those living above poverty (8.4% compared to 3.1%, respectively). McMahon JH, Elliott JH, Bertagnolio S, et al. For each NIS-Teen record, we used the available data to create new variables to document HPV vaccine initiation: not initiated, initiated at 910years of age, initiated at 1112years of age, initiated at 1314years of age, and initiated at 1517years of age. When data are available on a full census of the target population (e.g., through administrative records or public health surveillance), no sampling is needed. Does it vary among cities or neighborhoods? (e.g., influenza), Has it changed over the course of days? Risks can be calculated in the presence of late entries (left-truncation) and loss to follow-up (right-censoring) under strong assumptions about independence between entering/leaving the study and risk of the outcome (38, 39). Notably, among 1317-year-old adolescents in 2021, 89.6% received Tdap vaccination, 89.0% received MCV4 vaccination, but only 76.9% started the HPV vaccine series, with 61.7% up-to-date with the full HPV vaccine series.5. Incidence tells us something about how frequently an event occurs over time. There are multiple measures of incidence; in the interest of space, we will restrict our discussion to risks and rates. Future research looking at specific time differences between initiation and completion among birth cohorts and by age at initiation are needed to fully understand this issue. Sometimes the same variable can be measured using both a nominal scale and a ratio scale. Viral suppression is influenced by access to health care and is only possible if people are receiving antiretroviral therapy (except, in rare cases, for elite controllers) (41). Recommendations of the Advisory Committee on Immunization Practices (ACIP). Inappropriate adjustment may understate the magnitude of disparities (45) and adjusted statistics are prone to be interpreted causally, which could lead to inappropriate recommendations (9). Antiretroviral Therapy Cohort Collaboration, Vandenhende MA, Ingle S, et al. Measurement error can bias descriptive studies when we do not use, or there is no gold-standard measure of, the outcome. While only 4% of adolescents started HPV vaccination at 910years of age, these high series up-to-date status rates are in-line with prior research documenting similar patterns in a geographically-limited cohort of adolescents in Olmstead County Minnesota.32 However, the consistency of these findings with the Olmstead County study32 and other reports3334 lends support to efforts to begin HPV vaccination at the first opportunity as this may lead to greater coverage of the full vaccine series. Notably, as birth cohorts age into the recommended ages for HPV vaccination, high cohort-level HPV vaccine uptake is not typically seen for approximately three to four years, extending out to a substantial level of initiation at ages 1314years. HPV vaccine series initiation at 910years of age is low, but younger adolescents have a slightly higher proportion of initiation at this age group, possibly indicating some increased acceptance of this age for vaccination. Provides the basis for planning and evaluation of health services. We have multiple options for measures of occurrence, and like the proverbial blind men feeling the elephant, our choice of measure of occurrence might give us only part of the complete picture about the distribution of the outcome in the target population. Thus, the number of people with HIV infection may be inaccurate. To describe the occurrence, frequency, or relative frequency of an outcome, we need an unambiguous definition of that outcome, and we must be able to apply that definition in our data. Reagan-Steiner S, Yankey D, Jeyarajah J, Elam-Evans LD, Curtis CR, MacNeil J, Markowitz LE, Singleton JA. D. Is the basis of interpretation of experimental trials. All Rights Reserved. Example: We have clearly specified in our research question that we are interested in the prevalence of viral suppression on December 31, 2019. Notably, while there is very little difference by sex or age in uptake of Tdap or MCV4 vaccines, marked differences are seen for both initiation and series up-to-date status for HPV vaccines. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. Future efforts should evaluate how this can be incorporated into clinical practice, while also acknowledging that some healthcare practices that have had success in bundling all three adolescent vaccines at 1112years of age should be supported to continue what is working for them. Describe any relevant features of the place and time in which the target population resides and across which data were collected. In certain field investigations, identifying the cause is sufficient; if the cause can be eliminated, the problem is solved. (a) Describe the primary statistical methods used to estimate the measure of disease occurrence being targeted; discuss assumptions of that method in light of data limitations (e.g., assumption of independent censoring for people lost to follow-up). For children of parents who consent, providers are contacted to supply vaccination data for the adolescent. Learn about the veterinary topic of Basic Principles of Epidemiology. We summarize guidance provided herein in Table 1 in the form of a checklist modeled after the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines (3). For permissions, please e-mail: journals.permissions@oup.com. Failure to suppress viral load below a lower threshold may also be a more sensitive indicator of subsequent morbidity and mortality (2428), but suppression below a higher threshold is more relevant as an indicator of an individuals transmission potential (29, 30), so our choice of threshold may depend on how our results will be used. The incidence of some cancers has varied over time as a result of changes in behavior or diagnostic methods and treatment. CDC twenty four seven. Consider the following examples: Descriptive epidemiology provides a way of organizing and analyzing data on health and disease in order to understand variations in disease frequency geographically and over time and how disease varies among people based on a host of personal characteristics (person, place, and time).
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