An outcome study of the use of computed tomography for the diagnosis of appendicitis in a community-based emergency department.Objectives: Previous studies evaluating the use of CT in the diagnosis of appendicitis Appendicitis Definition Appendicitis is an inflammation of the appendix, which is the worm-shaped pouch attached to the cecum, the beginning of the large intestine. The appendix has no known function in the body, but it can become diseased. have taken place at university-based institutions where surgical bedside consultation seems prudent before radiological study. In the private hospital setting, the emergency department (ED) physician is responsible for diagnosis. We attempt to assess if this process is detrimental to patient care. Methods: Retrospective review retrospective review, a posttreatment assessment of services on a case-by-case or aggregate basis after the services have been performed. of 150 patient's records admitted through the ED was performed with the discharge diagnosis of appendicitis between March 1998 and May 2000. Data was stratified stratified /strat·i·fied/ (strat´i-fid) formed or arranged in layers. strat·i·fied adj. Arranged in the form of layers or strata. for analysis based on age (< 15, 15-50, > 50) and gender. Using Graph Pad Prism software the groups were compared for complications based on whether or not CT was obtained. Chi-square, number needed to treat number needed to treat Decision-making The minimum number of Pts to whom a particular intervention must be administered in a trial or controlled study to prevent a single target event. See Absolute risk reduction, Odds ratio, Relative risk reduction, Threshold NNT. (NNT NNT Number needed to Treat (medical) NNT Numero Necesario a Tratar (Spanish: number needed to treat) NNT Nassim Nicholas Taleb (author, essayist) NNT Neural Network Toolbox ), absolute risk reduction (ARR ARR See: Average rate of return ), relative risk reduction (RRR See Required Rate of Return. ) and respective confidence intervals were calculated for each group. Results: No significant differences overall were obtained between CT and no CT groups at P < 0.05. A significant benefit is demonstrated at P = 0.017 in females of childbearing age while a detrimental trend is found for those over the age of 50 years. Conclusions: Contrary to our initial hypothesis, no increased incidence of appendiceal perforation per·fo·ra·tion n. 1. The act of perforating or the state of being perforated. 2. An abnormal opening in a hollow organ or viscus, as one made by rupture or injury. Perforation A hole. or abscess abscess, localized inflamation associated with tissue necrosis. Abscesses are characterized by inflamation, which is due to the accumulation of pus in the local tissues, and often painful swelling. was demonstrated based on the ED physician's decision to perform CT without surgical consultation. Key Words: appendicitis, CT scan CT scan: see CAT scan. See CAT scan. , gynecological gynecological /gy·ne·co·log·i·cal/ (-kah-loj´i-k'l) gynecologic. misdiagnosis mis·di·ag·no·sis n. pl. mis·di·ag·no·ses An incorrect diagnosis. mis·di  ag·nose
********** In the past decade, much research has been dedicated to the radiological evaluation of patients presenting to emergency departments with abdominal pain Abdominal pain can be one of the symptoms associated with transient disorders or serious disease. Making a definitive diagnosis of the cause of abdominal pain can be difficult, because many diseases can result in this symptom. Abdominal pain is a common problem. where acute appendicitis is a major focus of the differential diagnosis differential diagnosis n. Determination of which one of two or more diseases with similar symptoms is the one from which the patient is suffering. Also called differentiation. . There exists an argument as to the proper use of computed tomography Computed tomography (CT scan) X rays are aimed at slices of the body (by rotating equipment) and results are assembled with a computer to give a three-dimensional picture of a structure. in the diagnostic paradigm. The majority of this debate has taken place at radiology and surgery programs at large university-based hospitals where surgical teams are readily available for bedside patient care and observation. A different scenario exists in community-based hospitals where surgeons rely on emergency department evaluation and diagnosis. Importance With the evolving technology of CT, including high-resolution spiral CT Spiral CT Also referred to as helical CT, this method allows for continuous 360-degree x-ray image capture. Mentioned in: Computed Tomography Scans , the abdomen and pelvis can be visualized in a relatively short period of time. For a suspected diagnosis of appendicitis, radiological studies have documented sensitivities of 90 to 100%, specificities of 91 to 99%, positive predictive values Positive predictive value (PPV) The probability that a person with a positive test result has, or will get, the disease. Mentioned in: Genetic Testing positive predictive value of 95 to 97%, and accuracies of 94 to 100%. (1-7) A study of patients presenting with atypical symptoms in 1998 yielded impressive results for CT scanning CT scanning Computer tomography scanning is a diagnostic imaging tool that uses x rays sent through the body at different angles. Mentioned in: Apraxia , which appeared to change the ED management for abdominal pain patients. (2,8-9) Considering the negative aspects of patient morbidity and mortality Morbidity and Mortality can refer to:
Appendectomy is the surgical removal of the appendix. The appendix is a worm-shaped hollow pouch attached to the cecum, the beginning of the large intestine. rate, diminish patient cost factors, and provide a surgical guide for intervention in complicated cases. (6-8,10-13) Furthermore, it can provide alternative diagnoses in patients found to be negative for the disease. This is of particular importance in women of childbearing age. Others argue that the procedure does not diminish perforation rates, may delay diagnosis, and should only be ordered after surgical consultation and evaluation. (9,15-23) Goals Of This Investigation In a community hospital emergency department setting, the on-call general surgeon General surgeon A physician who has special training and expertise in performing a variety of operations. Mentioned in: Appendectomy is not always physically able to evaluate all patients presenting with symptoms suggestive of suggestive of Decision making adjective Referring to a pattern by LM or imaging, that the interpreter associates with a particular–usually malignant lesion. See Aunt Millie approach, Defensive medicine. appendicitis. The diagnosis thus becomes the responsibility of the emergency department physician. To evaluate the role of contrast-enhanced CT in this process at our facility, we retrospectively analyzed patient outcomes during a period of increased diagnostic use in the emergency department. We hypothesized that the delay required for CT evaluation before surgical intervention would result in increased patient complications. Materials and Methods Setting Our not-for-profit hospital is a community-based, tax-supported hospital serving a small urban population. The stable population of the area is approximately 300,000. Single coverage surgical call is provided by 12 general surgeons from a private group practice, an HMO-based group, and 2 single practitioners. Twenty four hour response is required regardless of the surgeon's private patient responsibilities or scheduled surgery. CT is available 24 hours a day utilizing a double contrast protocol. Patients are required to ingest in·gest tr.v. in·gest·ed, in·gest·ing, in·gests 1. To take into the body by the mouth for digestion or absorption. See Synonyms at eat. 2. oral contrast over an approximate 2 hour period before imaging. IV contrast is then administered and 5 mm sequential views are created through the abdomen and pelvis. Selection of participants Approval was received from the hospital institutional review board for this retrospective chart review. All records of patient charts from the institution with a diagnosis code of appendicitis from March 1998 to May 2000 were examined. This time period was selected based on a review of the literature regarding appendicitis management. Published surgical and radiology articles were beginning to support the diagnostic role of CT in appendicitis. (1-3, 6-8) It was our aim to gather data before this accepted standard of care to objectively inspect the outcome trends related to the use of CT in the diagnosis of appendicitis. Only those patients who were admitted through the emergency department were utilized and direct admissions were excluded. Patients less than 3 years of age and greater than 80 years were not included in the sample of patients. Exclusion criteria exclusion criteria AIDS Donor exclusion criteria, see there also included charts with incomplete details of event time recordings. This criterion was essential to compare durations of procedures and possible links to complications between those patients who underwent CT evaluation and those who did not. Of 150 charts, 7 were excluded from the chart review for not meeting this criterion. The final sample (n = 143) consisted of 87 males and 56 females. The average age was 33.2 years with a range of 7 to 78 years. Data collection and processing Patient charts were examined for age, sex, date, and time of admission from the ED. The time of initial ED physician examination was recorded and used to evaluate elapsed time e·lapsed time n. The measured duration of an event. Noun 1. elapsed time - the time that elapses while some event is occurring to the following pertinent events: order time of CT, time to operation, time of first antibiotic dose, and date and time of discharge from the hospital. Times were rounded to the nearest 15 minutes. Any complication was also noted (ie, perforation, abscess, rupture) though not characterized with regards to severity. Outcome values were entered into a spreadsheet and the data was analyzed after separating subjects into groups based on whether or not a CT scan was performed. Of the 143 total patient sample, 87 received the procedure. The average age was 33.1 ([+ or -] 18.9) years and 33.3 ([+ or -] 16.9) years for the CT and no CT (NCT NCT National Childbirth Trust NCT National Car Test NCT North Carolina Theatre NCT National Coordination Team NCT Northern California TRACON NCT Noise Cancellation Technology NCT Network Control and Timing NCT Nicotine Replacement Therapy ) groups respectively. As previously stated, the initial time of ED physician examination was used as the central data point from which all other measures were compared. This helped to eliminate deviations in time due to factors beyond the control of hospital staff. To minimize other possible confounding confounding when the effects of two, or more, processes on results cannot be separated, the results are said to be confounded, a cause of bias in disease studies. confounding factor factors, all patient interventions were assessed with respect to the times annotated on the charts by the ordering physicians. Stratification of the data was further performed specific to those less than 15 years of age, all patients greater than 15 years of age, sex and age between 15 and 50 years, and those patients greater than 50 years of age. Females between 15 and 50 years of age have been recognized in previous studies (12,14-15) to be of childbearing age and are associated with more complicated differential diagnoses when considering pelvic pathology. Males and females between these ages were subsequently compared based on whether or not a CT was performed and if an adverse event was encountered. Results Table 1 demonstrates absolute values for stratified groups including number and percent of complications. Using Graph Pad Prism software (San Diego San Diego (săn dēā`gō), city (1990 pop. 1,110,549), seat of San Diego co., S Calif., on San Diego Bay; inc. 1850. San Diego includes the unincorporated communities of La Jolla and Spring Valley. Coronado is across the bay. , CA) the pertinent times for patient interventions (timing of antibiotics, time of operation, and time to discharge) were compared using an unpaired t test. No significant differences were discovered between the CT and NCT groups (Table 2). To evaluate the incidence of complications between all patients who received CT versus the NCT group, a [chi square chi square (kī), n a nonparametric statistic used with discrete data in the form of frequency count (nominal data) or percentages or proportions that can be reduced to frequencies. ] test was used and revealed no differences (P = 0.124). When comparing complications between CT and NCT groups in the stratified data a significant difference (P = 0.017) was found for females 15 to 50 years age. Only 9.1% of the CT group encountered complications compared with 46.7% of the NCT group. This equated to an absolute risk reduction (ARR) of 37.6% with confidence interval (CI) of 9.62%-65.53% at 95%. This indicates that 33.3% [number needed to treat (NNT) = 3, 95% CI = 1.5-10.4] of females aged 15 to 50 years benefited from receiving a CT scan. An identical comparison of males in this age range yielded P = 0.20 and nothing significant with respect to NNT and ARR. In patients older than 50 years, a trend toward increased risk of complications is demonstrated for those who underwent CT compared with those who did not. The chi-square analysis for this group was not significant at P = 0.70, however 40.0% of patients who underwent CT evaluation suffered complications, versus 30.0% of those who did not have CT evaluation. Ten percent of patients in this age group are therefore potentially harmed by the procedure. All statistical results are delineated in Table 3. Discussion The sensitivities and specificities for the CT diagnosis of appendicitis in both the university-based hospital (1-2,7,11-14) and community hospital settings (3,5) have been well documented. To our knowledge, no studies in community ED environments have evaluated patient outcomes in the adult population. Ours is the first to examine this perspective. We analyzed the consequences of using CT as a diagnostic aid in patients with acute appendicitis in the private hospital sector. This is important as many emergency department physicians practice in an isolated environment without immediate surgical input. In the university-based setting, the preferred practice is to consult the surgical on-call service for bedside evaluation and determination of the need for radiological study before laparotomy laparotomy /lap·a·rot·o·my/ (-rot´ah-me) incision through the flank or, more generally, through any part of the abdominal wall. lap·a·rot·o·my n. 1. . (15-17,21-22) The implications of our results may impact community ED practice behavior. Contrary to our initial hypothesis, no increased incidence of perforation or abscess was found in patients with the discharge diagnosis of appendicitis who underwent CT as a diagnostic aid in comparison to those patients who did not undergo the procedure. Furthermore, no significant delays were demonstrated for times to antibiotic administration, operating room operating room n. Abbr. OR A room equipped for performing surgical operations. arrival, and time of discharge from the hospital in patients undergoing the procedure. The largest absolute risk reduction for perforation was found for women considered to be of menstruating men·stru·ate intr.v. men·stru·at·ed, men·stru·at·ing, men·stru·ates To undergo menstruation. [Late Latin m , childbearing age. Since only patients with appendicitis were analyzed, the assumption can be made that CT evaluation in this group of patients avoided gynecological misdiagnoses inherent without the benefit of CT scanning. This result comes as no surprise and substantiates previous studies evaluating the value of CT in women of this age group. (11-12,25-26) Increased risk for perforation was found for those over the age of 50 who underwent CT versus those who did not. Overall data supports no increased complications for those who undergo CT evaluation for appendicitis. Other explanations are more plausible for the results in this age group. Vague history and subjective symptoms, late presentations, and equivocal EQUIVOCAL. What has a double sense. 2. In the construction of contracts, it is a general rule that when an expression may be taken in two senses, that shall be preferred which gives it effect. Vide Ambiguity; Construction; Interpretation; and Dig. physical examinations are perhaps causative caus·a·tive adj. 1. Functioning as an agent or cause. 2. Expressing causation. Used of a verb or verbal affix. caus . A combination of these factors is suspected and deserves further separate investigation. The retrospective nature of this study reveals inherent limitations that are unavoidable. These revolve around Verb 1. revolve around - center upon; "Her entire attention centered on her children"; "Our day revolved around our work" center, center on, concentrate on, focus on, revolve about human errors of reliance on chart data documentation and collection with a possible inability to decipher decision-making after care is given. A bias of retrospective examination that must be considered is that patients who appeared more ill might have been taken to the OR without CT examination, resulting in a higher complication rate in the NCT group. A factor not established was whether a surgeon was involved in the decision to order CT evaluation. Individual cases may have had surgical input that was not evident retrospectively. This is not the normal situation at our institution given the office and operating responsibilities of any staff physician. In addition, in the private sector, on-call physicians are often reluctant to respond until a definitive diagnosis has been made in the emergency department. Conclusion The diagnosis of appendicitis is relatively straightforward in those patients presenting with the classic symptoms of abdominal pain of short duration, migration to the right lower quadrant right lower quadrant Physical exam The region of the abdomen that contains the terminal ileum, appendix and cecum , and anorexia. Atypical presentations, however, occur in approximately 30% of patients, (6,24) often at the extremes of age and the female gender. We hypothesized that the increased use of CT for the diagnosis of appendicitis in the emergency department setting would result in increased complications from a patient outcome standpoint. On the contrary we found that its use does not negatively impact patient outcome in a community-based hospital setting where diagnosis is most frequently in the hands of the emergency department physician. References 1. Rao PM, Rhea rhea, in zoology rhea (rē`ə), common name for a South American bird of the family Rheidae, which is related to the ostrich. Weighing from 44 to 55 lb (20–25 kg) and standing up to 60 in. JT, Novelline RA, et al. Helical helical /hel·i·cal/ (hel´i-k'l) spiral (1). hel·i·cal adj. 1. Of or having the shape of a helix; spiral. 2. Having a shape approximating that of a helix. CT technique for the diagnosis of Appendicitis: Prospective evaluation of a focused appendix CT examination. Radiology 1997;202:139-144. 2. Rao PM, Rhea JT, Novelline RA, et al. Effects of computed tomography of the appendix on treatment of patients and use of hospital resources. N Engl J Med 1998;338:141-146. 3. Funaki B, Grosskreutz SR, Funaki CN. Using unenhanced helical CT with enteric enteric /en·ter·ic/ (en-ter´ik) within or pertaining to the small intestine. en·ter·ic adj. 1. Of, relating to, or within the intestine. 2. contrast material for suspected appendicitis in patients treated at a community hospital. AJR AJR American Journal of Roentgenology AJR American Journalism Review AJR Academy for Jewish Religion AJR Association of Jewish Refugees (UK organization) AJR Accelerated Junctional Rhythm 1998;171:997-1001. 4. Paulson EK, Kalady MF, Pappas TN. Suspected appendicitis. N Engl J Med 2003;348:236-242. 5. Malone AJ, Wolf CR, Malmed AS, et al. Diagnosis of acute appendicitis: Value of unenhanced CT. AJR 1993;160:763-766. 6. Birnbaum BA, Jeffrey RB. CT and sonographic evaluation of acute right lower quadrant abdominal pain. AJR 1998;170:361-371. 7. Balthazar EJ, Megibow AJ, Siegel SE, et al. Appendicitis: Prospective evaluation with high-resolution CT. Radiology 1991;180:21-24. 8. Neumayer L, Wako E, Fergestaad J, et al. Impact of journal articles and grand rounds on practice: CT scanning in appendicitis. J Gastrointest Surg 2002;6:338-341. 9. Morris KT, Kavanagh M, Hansen P, et al. The rational use of computed tomography scans Computed Tomography Scans Definition Computed tomography (CT) scans are completed with the use of a 360-degree x-ray beam and computer production of images. These scans allow for cross-sectional views of body organs and tissues. in the diagnosis of appendicitis. Am J Surg 2002;183:547-550. 10. Raptopoulos V, Katsou G, Rosen MP, et al. Acute Appendicitis: Effect of increasing use of CT on selecting patients earlier. Radiology 2003;226:521-526. 11. Fuchs JR, Schlamberg JS, Shortsleeve MJ, et al. Impact of abdominal CT imaging on the management of appendicitis: An update. J Surg Res 2002;106:131-136. 12. Balthazar EJ, Rofsky NM, Zucker R. Appendicitis: The impact of computed tomography imaging on negative appendectomy and perforation rates. Am J Gastroenterol 1998;93:768-771. 13. Stroman DL, Bayouth CV, Kuhn JA, et al. The role of computed tomography in the diagnosis of acute appendicitis. Am J Surg 1999;178:485-489. 14. Balthazar EJ, Birnbaum BA, Yee J, et al. Acute appendicitis: CT and US correlation in 100 patients. Radiology 1994;190:31-35. 15. Johnson D, editor. World literature review: Diagnosis of acute right lower quadrant pain and appendicitis by CT scan: Do we still need the clinician? Am J Gastroenterol 2000;95:1355-1357. 16. Safran DB, Pilati D, Folz E, et al. Is appendiceal CT scan overused for evaluating patients with right lower quadrant pain? Am J Emerg Med 2001;19:199-203. 17. McDonough J, Stasik C, Piontkowsky D, et al. Can appendiceal CT scanning be utilized effectively in widespread general surgical practice? Am Surg 2002;68:917-921. 18. Weyant MJ, Eachempati SR, Maluccio MA, et al. The use of computed tomography for the diagnosis of acute appendicitis in children does not influence the overall rate of negative appendectomy or perforation. Surg Infect 2001;2:19-23. 19. Karakas SP, Guelfquat M, Leonidas JC, et al. Acute appendicitis in children: Comparison of clinical diagnosis with ultrasound and CT imaging. Pediatr Radiol 2000;30:94-98. 20. Flum DR, Morris A, Koepsell T, et al. Has misdiagnosis of appendicitis decreased over time? JAMA JAMA abbr. Journal of the American Medical Association 2001;286:1748-1753. 21. McDonald GP, Pendarvis DP, Wilmoth R, et al. Influence of preoperative pre·op·er·a·tive adj. Preceding a surgical operation. preoperative preceding an operation. preoperative care the preparation of a patient before operation. computed tomography on patients undergoing appendectomy. Am Surg 2001;67:1017-1021. 22. Perez J, Barone JE, Wilbanks TO, et al. Liberal use of computed tomography scanning does not improve diagnostic accuracy in appendicitis. Am J Surg 2003;185:194-197. 23. Lee SL, Walsh AJ, Ho HS. Computed tomography and ultrasonography ultrasonography /ul·tra·so·nog·ra·phy/ (-so-nog´rah-fe) the imaging of deep structures of the body by recording the echoes of pulses of ultrasonic waves directed into the tissues and reflected by tissue planes where there is a change in do not improve and may delay the diagnosis and treatment of acute appendicitis. Arch Surg 2001;136:556-562. 24. Lewis FR, Holcroft JW, Boey J, et al. Appendicitis: A critical review of diagnosis and treatment in 1000 cases. Arch Surg 1975;110:677-681. 25. Bendeck SE, Nino-Murcia M, Berry GJ, et al. Imaging for suspected appendicitis: Negative appendectomy and perforation rates. Radiology 2002;225:131-136. 26. Naoum JJ, Mileski WJ, Daller JA, et al. The use of abdominal computed tomography scan Computed tomography scan (CT scan) A specialized type of x-ray imaging that uses highly focused and relatively low energy radiation to produce detailed two-dimensional images of soft tissue structures, particularly the brain. decreases the frequency of misdiagnosis in cases of suspected appendicitis. Am J Surg 2002;184:587-589. Robert D. Mathis, MD, Andrea B. Chiumento, MD, MS, Benson Yeh, MD, and Nita Dollieslager, RN From the Department of Emergency Services emergency services Emergency care '…services …necessary to prevent death or serious impairment of health and, because of the danger to life or health, require the use of the most accessible hospital available and equipped to furnish those services' , Halifax Medical Center Halifax Medical Center (HMC) is a 764-bed hospital located in Daytona Beach, Florida. HMC is the largest hospital serving Volusia and Flagler counties and provides the area's only trauma center, pediatric emergency department, neonatal intensive care unit and pediatric intensive , Daytona Beach Daytona Beach (dātō`nə), city (1990 pop. 61,921), Volusia co., NE Fla., on the Atlantic coast and Halifax River (a lagoon); inc. 1876. Center of a rapidly urbanizing area, in a region settled by Spanish Franciscans in the 17th cent. , FL and the Department of Emergency Medicine, The Brooklyn Hospital Center, Brooklyn, NY. Reprint requests to Andrea B. Chiumento, P.O. Box 9071, Daytona Beach, FL 32120. Email: rmathis1@cfl.rr.com Accepted August 25, 2005. RELATED ARTICLE: Key Points * In the community hospital setting, bedside surgical consultation is not always available and the decision to utilize CT evaluation for the diagnosis of appendicitis becomes the responsibility of the ED physician. * CT evaluation of the patient presenting emergently with abdominal pain has its greatest utility for those with atypical symptoms, age of presentation, and female gender. * Perceived delays in the diagnosis of appendicitis utilizing CT imaging are not detrimental to patients presenting emergently in the community hospital-based setting.
Table 1. Stratified groups including number and percent of
complications (a)
CT + cx NCT + cx
CT [n (%)] NCT [n (%)]
All (n = 143) 87 18 (20.7) 56 18 (32.1)
All > 50 years (n = 30) 20 8 (40.0) 10 3 (30.0)
All [greater than or equal to] 70 12 (17.1) 44 14 (31.8)
15 years (n = 114)
All < 15 years (n = 29) 17 6 (35.3) 12 4 (33.3)
F 15-50 years (n = 37) 22 2 (9.1) 15 7 (46.7)
M 15-50 years (n = 47) 28 2 (7.1) 19 4 (21.1)
(a) cx, complications; NCT, no CT; F, female; M, male.
Table 2. Comparison of intervention times (a)
CT (n = 87) NCT (n = 56)
Age (yrs.) 33.1 33.3
Time to CT (hr:min) 1:55 n/a
Time to OR (hr:min) 14:53 16:35
Time to Abx (hr:min) 5:31 2:19
Hospital stay (hr:min) 56:45 67:15
Complications 20.7% (n=18) 32.1% (n=18)
(a) NCT, no CT; Abx, antibiotics..
Table 3. Statistical results (a)
P value NNT 95% CI (%)
All (n = 143) 0.124 12 NS
All > 50 years (n = 30) 0.702 (10) (b) NS
All [greater than or equal to] 15 years 0.107 7 NS
(n = 114)
All < 15 years (n = 29) 1.00 51 NS
F 15-50 years (n = 37) 0.017 3 1.5 to 10.4
M 15-50 years (n = 47) 0.204 8 NS
ARR (%) 95% CI (%)
All (n = 143) 8.94 -5.92 to 23.80
All > 50 years (n = 30) (10.00) (b) -25.60 to 45.60
All [greater than or equal to] 15 years 14.68 -1.68 to 31.03
(n = 114)
All < 15 years (n = 29) 1.96 -33.07 to 37.00
F 15-50 years (n = 37) 37.58 9.62 to 65.53
M 15-50 years (n = 47) 13.91 -6.76 to 34.57
(a) NNT, number needed to treat; ARR, absolute risk reduction; NS, no
significance [as a 95% CI for NNT cannot be calculated when the 95% CI
for ARR extends from a negative (harmful result) to a positive
(beneficial result).] F, female; M, male.
(b) Represents NNT for a harmful event and an absolute risk increase for
this group.
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