F
Filomena Pereira-Maxwell in Medical Statistics, 2018
A clinical trial or epidemiological study in which information is collected by following study participants over a period of time, thus allowing temporal relationships to be investigated. The terms prospective and longitudinal are sometimes used as synonymous with follow-up study, but the former simply indicates that a study is conducted looking forward in terms of data collection and occurrence of events, even when there is no follow-up in the usual sense of the expression (e.g. prospective nested case-control study). On the other hand, a retrospective cohort study is a longitudinal study, although study participants are not actually followed up as all exposures and events of interest have already taken place. Follow-up studies are often concerned with estimating the incidence over time of some occurrence or disease, or the average ‘time to event’ and/or probability of survival.
Understanding Studies of Resistant Organisms: Focus on Epidemiologic Methods
Robert C. Owens, Lautenbach Ebbing in Antimicrobial Resistance, 2007
In a cohort design, patients are entered into the study based on the presence or absence of an exposure (or risk factor) of interest (Fig. 1). These two groups (i.e., those with the exposure and those without the exposure) are then compared to determine if they differ with regard to development of the outcome of interest. Whether a cohort study is prospective or retrospective depends on when it is conducted with regard to when the outcome of interest occurs. If patients are identified as exposed or unexposed and then followed forward in time to determine whether they develop the outcome, it is a prospective cohort study. If the study is conducted after all outcomes have already occurred, it is a retrospective cohort study. As an example, one might identify all patients who receive a FQ in the hospital (i.e., the exposed) and compare them to patients who do not receive a FQ (i.e., the unexposed). These groups could then be followed forward to determine what proportion of patients in each group develops the outcome of interest (i.e., FQREC infection).
Observational Studies
Abhaya Indrayan in Research Methods for Medical Graduates, 2019
The dominant format of a retrospective study is case–control, in which subjects with and without disease are investigated for past exposure. Those suffering from the disease or who have the health condition of interest are called cases, and those without that particular health condition are called controls. All case–control studies are retrospective, but not all retrospective studies are all case–control studies. Investigating the past history of cases of myocardial infarction is a retrospective study, but there may not be any control. Then it is not a case–control study. Obtaining the history of cervical cancer patients regarding infections, diet, and use of oral contraceptives is retrospective but not a case–control study if noncancer subjects are not part of the study. However, a control group provides a legitimate base for attributing differences in the two groups to the antecedents, such as high cholesterol level and obesity in patients with myocardial infarction – thus, the case–control setup is considered a natural format for retrospective studies.
Microwave ablation of hepatic malignant tumors using 1.5T MRI guidance and monitoring: feasibility and preliminary clinical experience
Published in International Journal of Hyperthermia, 2019
Zhengyu Lin, Jin Chen, Yuan Yan, Jian Chen, Yuliang Li
The present study has certain shortcomings. Our study is a retrospective study. MRI is a more complex procedure compared with CT or US, and the present study lacked comparison with other guiding modalities. Patients with pacemakers or metal implants cannot undergo MRI. The 35 s monitoring imaging using temporal resolution was not real-time. Our study used closed MRI, although this procedure ensured high field strength, fast imaging, and image clarity, the operation time was prolonged because of the need to repeatedly move the examination bed during the procedure. In addition, temperature-measurement software was not used to monitor the ablation process in real time. Finally, the study included only 35 patients with 48 lesions and had a short follow-up duration, because the purpose of this study was to determine the feasibility of MRI-guided and monitored MWA of hepatic malignant tumors. In future studies, a larger sample size and a longer follow-up will be required to explore the clinical significance of this technique.
Comparison of Right-side and Left-side Colon Cancers Following Laparoscopic Radical Lymphadenectomy
Published in Journal of Investigative Surgery, 2021
Han Deok Kwak, Jae Kyun Ju, Soo Young Lee, Chang Hyun Kim, Young Jin Kim, Hyeong Rok Kim
This retrospective study used prospective data for analysis. Between December 2009 and December 2014, 966 patients who underwent radical lymph node dissection were included. The right colon group included cecal, ascending, and hepatic flexure colon cancers, while the left colon group included splenic flexure, descending, sigmoid, and rectosigmoid junction colon cancers. The transverse colon is the boundary between midgut and hindgut, with no definite consensus in the literature on the origin, which is either the one-third or mid-portion of the transverse colon. The rectum, which is the transitional area between the hindgut and cloaca, was also excluded. In addition, patients with synchronous or multiple cancers and those with fewer than 12 harvested nodes, which could affect the comparison of sidedness, were also excluded. As most of the cases were performed with laparoscopic surgery, this analysis excluded open surgery, which represented <10%.
Management of complicated skin and skin structure infections – a call for infectious disease specialists
Published in Infectious Diseases, 2018
The vast number of studies on ID specialist consultation seems to reflect a difficulty to perform controlled randomized studies. The limitations are obvious, including selection bias and problems associated with unattainability of blind performance. Much data is based on observations before vs. after the introduction of ID specialist service [4,5], the obvious limitation being a difficulty to control for changes besides those attributed to the implementation of ID specialist service. Due to difficulties to conduct stringent comparative studies, there is a room for additional approaches. One such example is the real-life study on complicated skin and skin structure infections by Jääskeläinen et al. reported in the present issue of Inectious Diseases. The term ‘real-life’ implicates observations performed in everyday care and their study comprised data obtained in two geographical areas within one and the same time frame. An advantage was a lack of influence by the announcement of a formal study and the subsequent awarenesss among actors and attention on what they were doing. Disadvantages were those associated with a retrospective study, i.e. lack of randomization and control.
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