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General Surgery
Published in Tjun Tang, Elizabeth O'Riordan, Stewart Walsh, Cracking the Intercollegiate General Surgery FRCS Viva, 2020
Rebecca Fish, Aisling Hogan, Aoife Lowery, Frank McDermott, Chelliah R Selvasekar, Choon Sheong Seow, Vishal G Shelat, Paul Sutton, Yew-Wei Tan, Thomas Tsang
What biases exist in a screening programme?Lead-time bias − survival is measured from detection to death, and this will be longer because the disease is detected earlier.Selection bias − individuals who present for screening are more likely to be health conscious and may not represent a true sample of the population.Length bias − slow-growing tumours are more likely to be detected by screening than rapidly growing tumours, which would present between screening intervals.
Screening
Published in S Asbury, A Mishra, KM Mokbel, M Fishman Jonathan, Principles of Operative Surgery, 2017
S Asbury, A Mishra, KM Mokbel, M Fishman Jonathan
When evaluating screen-detected cancers, three types of inherent bias are involved. Lead time bias. Survival measured from detection to death will be longer if the cancer is detected earlier, irrespective of any alteration in the disease process.Selection bias. Individuals who take up the offer of screening tend to be more health-conscious and therefore more likely to live longer for reasons unrelated to the detected disease.Length bias. Slow-growing indolent tumours are more likely to be detected by screening than rapidly growing tumours that arise and become symptomatic between screening intervals.
Audit, research and management
Published in Marwan Habiba, Andrea Akkad, Justin Konje, MRCOG Part 2, 2017
Marwan Habiba, Andrea Akkad, Justin Konje
C. Screening bias is a type of selection bias which occurs in screening programmes; those who comply with a screening programme tend to be generally healthier and at a lower risk compared to non-participants. There are a number of reasons for this, including socio-demographic factors. There is a risk that the better outcome noted in participants be wrongly attributed to the screening programme. Length, or length-time, bias occurs in diseases which present across a broad spectrum of biologic activity; some patients have aggressive, rapidly growing tumours with a short asymptomatic phase, whilst others have less aggressive tumours with longer latency and an inherently better prognosis. These less aggressive tumours will be more likely to be identified in a screening programme, and, even without therapy, the cohort identified by screening will have a better prognosis. Lead-time bias occurs when the disease has a long asymptomatic period which is not taken into account. Here, it is possible that screening may result in early diagnosis, but the natural history remains unaltered, for example because of the absence of effective intervention.
Disparity in use of modern combination chemotherapy associated with facility type influences survival of 2655 patients with advanced pancreatic cancer
Published in Acta Oncologica, 2022
Morten Ladekarl, Louise Skau Rasmussen, Jakob Kirkegård, Inna Chen, Per Pfeiffer, Britta Weber, Halla Skuladottir, Kell Østerlind, Jim Stenfatt Larsen, Frank Viborg Mortensen, Henriette Engberg, Henrik Møller, Claus Wilki Fristrup
Fewer patients were included in the standardized cancer pathway at tertiary centers compared to secondary centers (74 versus 79%). We hypothesize that patients at tertiary facilities may more often be diagnosed incidentally, thus not being registered for a cancer-specific pathway. This may imply a minor lead time bias favoring survival in tertiary facilities. The, on average, 3 day longer delay in treatment start observed at tertiary centers did not result in inferior survival measured from start of chemotherapy. Possible lead time bias prior to any contact of the patient with the health system (and its association with facility type) could not be assessed. The work up procedures and guarantied waiting times in the standardized cancer pathway were, however, unchanged during the inclusion period, and we found no indications of diagnosis at an earlier stage with respect to stage (M-stage) during the latter years of the inclusion period for the whole cohort or according to facility type (data not shown).
The Increasing Proportion of Early-Stage Pancreatic Cancer between 2004–2013: A SEER Analysis
Published in Cancer Investigation, 2021
Sven P Oman, Juan E Corral, John Stauffer, Massimo Raimondo, Kabir Mody, Michael Wallace
The strengths of our study are several. The SEER database is a large repository, which includes about a third of the United States population and is demographically representative. We examined a 10-year period of time, which captured trends in the incidence of cancer. However, our results do have limitations inherent to retrospective research, and changes in staging and reporting patterns cannot be excluded based on SEER available variables. We recognize that the mortality of many individuals may not change despite diagnosis at an earlier stage, and further research adjusting for late time and lead time bias is required. Our results are limited by poor reporting of AJCC stage across the SEER registry and other types of selection bias, though when the analysis was repeated for the entire database, including cases without stage detail, a similar correlation coefficient was maintained. Our results are limited to the United States and cannot be generalized to low and middle-income countries. Indeed, pancreatic cancer incidence rates are higher in North America and Europe compared to Africa, though this may be confounded by differences in diagnostic use and reporting patterns (2).
Prostate cancer specific mortality after 5α-reductase inhibitors medication in benign prostatic hyperplasia patients: systematic review and meta-analysis
Published in The Aging Male, 2021
Jae Joon Park, Hyun Young Lee, Sung Ryul Shim, Sang Wook Lee, Kwang Taek Kim, Jae Heon Kim
Among the studies included in our meta-analysis, Sarker et al.'s 2019 study [26] had exceptionally high rates of death from cancer and from all causes. Conceivable causes of such high death rates include lead-time bias and misclassification. First, lead-time bias means that ifthe diagnosis is delayed, the time to death is short;so the deathrate for the disease may beoverestimated. We set the PSA of 4 ng/ml or more as the standard for elevated PSA to measure the time until prostate biopsy was done. This standard PSA value is higher than that of other included studies. So, in this study, the death rate may have been overestimatedbecause of lead-time bias. On the other hand, in this paper, we calculated the death rate from specific causesusing the National Death Index, but as mentioned, the cause of death may have been misclassified; so there may be differences from the actual rate of death from cancer. Considering these points, lower OR values may have been reported than we found in this meta-analysis; so5-ARI administration and deaths fromprostatecancer may have a lower association.