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Designing and Running a Clinical Trial
Published in Trevor F. Cox, Medical Statistics for Cancer Studies, 2022
Studies can be retrospective or prospective. Experimental studies are always prospective. Observational studies can be either. A cross-sectional study looks at data at one moment in time, or within a short time interval for practical reasons. A longitudinal study collects data at various time points.
Qualitative research in practice
Published in Jeremy Jolley, Introducing Research and Evidence-Based Practice for Nursing and Healthcare Professionals, 2020
Magilvy and Thomas (2009) point out that participants in qualitative studies must meet the following criteria:have experienced the phenomenon under examination;are able to communicate their experiences to the researcher;are willing to communicate their experiences. It can certainly be difficult to locate suitable participants and to find people who will agree to talk about issues that are important to them. It can also be difficult to retain participants in a study, especially if it is a more longitudinal study. While there is no need for the ‘sample’ to be representative of a population of similar people, researchers usually want to be able to argue that the conclusions to their study have relevance to other studies and to practice generally. Nevertheless, there are few of the sampling issues found in quantitative studies. We do not need to worry about a biased sample, we do not need to estimate what size of sample we will need and we certainly do not need a ‘large’ sample to convince others of the worth of our study.
Evidence for Genetic Predispositions for Criminogenic Behavior
Published in Gail S. Anderson, Biological Influences on Criminal Behavior, 2019
Another concern raised by Burt and Simons is common throughout criminology, and it is that many studies are based on the same data set. For example, in the 20 studies considered since 2008 by Burt and Simons, 17 used the US National Longitudinal Study of Adolescent Health (Add Health) data. Burt and Simons argued that despite this being an excellent and rich data set, any deficiencies are replicated in all studies.17 For example, they point out that measurements for delinquent peers are self-reports that ask the respondents to give their impressions of their three closest friends’ substance abuse of just three substances and that questions on bullying refer only to physical violence.17 This is interesting because in their rebuttal, Barnes and colleagues show that much of Simons’ own work is based on a single data set of only 800 respondents and that Simons has frequently praised the Add Health data set.19 Moreover, data sets such as Add Health and many others contain a very rich and large amount of data, which can be mined in many ways to answer a variety of questions and may not truly involve the same data.
A fusion learning method to subgroup analysis of Alzheimer's disease
Published in Journal of Applied Statistics, 2023
Mingming Liu, Jing Yang, Yushi Liu, Bochao Jia, Yun-Fei Chen, Luna Sun, Shujie Ma
In a longitudinal study, subjects are usually measured repeatedly over a time period. Suppose the data consist of ith subject are taken, and ith subject at time ith subject, we consider the subject-specific nonparametric regression model: t, and the errors 1) can be rewritten as
Association of Central Retinal Arteriolar and Venular Equivalents with Brain-aging and Macular Ganglion Cell-inner Plexiform Layer Thickness
Published in Ophthalmic Epidemiology, 2023
Adam J. Paulsen, Alex A. Pinto, Natascha Merten, Carla R. Schubert, Yanjun Chen, Barbara E.K. Klein, Stacy M. Meuer, Karen J. Cruickshanks
The consistency of these associations demonstrates retinal vessel measurements’ potential as neural retinal health indicators. As the mGCIPL was only measured for the first time at the 2015–2017 examination, this study cannot determine whether there is a temporal or potentially causal relationship between retinal vessel caliber and mGCIPL thickness. One potential pathway for this relationship could be narrower or restricted vessels lead to reduced blood flow and lower oxygen environments, resulting in neurodegeneration. Recent studies have implicated sleep apnea hypoxia in glaucoma neurodegeneration and in animal models retinal hypoxia induced by subarachnoid hemorrhage led to retinal ganglion cell loss.41,42 Additionally, CRAE and CRVE have been associated with atherosclerotic measures, such as pulse wave velocity.43,44 This may imply atherosclerotic processes impact neurodegeneration. Previous studies have not been able to establish the temporal relationships between changes in retinal vasculature and changes in microstructures such as the mGCIPL.45 Longitudinal study is needed to better understand these associations.
Understanding mother and child health-seeking behavior in urban Pakistan
Published in Health Care for Women International, 2022
Marina Haque, Allysha Choudhury, Alina Haque, Roland Alexander Blackwood
The first important study limitation is that data collection was limited to a span of two weeks and collected through convenience sampling because of very high safety concerns throughout Pakistan and the especially high security within the I-8 sector of Islamabad. This may have been too short of a time span for all participants to complete and return the survey, and may have contributed to the 14.2% non-response rate. However, many other studies in Pakistan have also reported similar limitations with regard to not being able to randomly sample women or having to limit their time collecting data due to safety or community concerns (Hamid, Stephenson, & Rubenson, 2011; NIPS, 2013). Another limitation is that respondents are primarily mothers who survived childbirth. A selection bias is likely present in this study for women who remained relatively able-bodied post-delivery. A final limitation is that a cross-sectional design leaves little room for causal inference of factors on health-seeking behavior. A longitudinal study can provide greater information onto the temporality of these factors.