***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: The Canadian National Breast Screening Study ( NBSS ) is a r and omized controlled trial to assess the effect of screening on breast cancer mortality . The NBSS design ated a single reference radiologist who blindly review ed over the course of the study 5200 r and omly selected two-view mammographic examinations of women not known to have breast cancer . He also review ed 575 screening-detected breast cancer ( SBC ) cases and 102 interval breast cancer ( IBC ) cases . All cancers were histologically proven . As a result of the review s , comments on inter-observer agreement , interpretation , and technical quality were conveyed on an ongoing basis to radiologists appointed to 15 NBSS screening centers .  Agreement of the reference radiologist with center radiologists was better for breast cancer cases ( kappa = 0.511 , P less than .002 ) than for those not known to have breast cancer ( kappa = 0.307 , P less than .002 ) . Observer error and technical problems led to delayed detection in 22 % of SBCs and 35 % of IBCs . Another 11 % of SBCs and 58 % of IBCs were probably mammographically occult . No similarly comprehensive review of mammography during a screening program has been published . Suggestions arising from the NBSS review were sometimes resisted by center radiologists . Measures are suggested which might facilitate acceptance of recommendations arising from audit mechanisms in mammography screening programs , thereby enhancing opportunities for mammographic excellence OBJECTIVES : To estimate women 's expectations of the accuracy of screening mammography and to explore attitudes towards compensation for missed cancers . DESIGN : Cross sectional survey ( by telephone ) . SETTING : Australia ; population -based survey conducted in April 1996 . PARTICIPANTS : R and om sample of women aged 30 - 69 years . A total of 2935 women completed the Breast Health Survey ( adjusted response rate 65 % ) . A r and om sample of 115 completed this sub-survey on perceived sensitivity of mammographic screening and compensation for missed cancers . RESULTS : About one third of women ( 32.2 % , 95 % CI 23.7 , 40.7 ) had an unrealistically high expectation of the sensitivity of screening mammography  , reporting it to be 95 % or higher . Approximately 40 % of the women ( 43.5 % , 95 % CI 34.4 , 52.6 ) thought that screening mammography should pick up all cancers ( should have a sensitivity of 100 % ) . Just under half the women ( 45.2 % , 95 % CI 36.1 , 54.3 ) said financial compensation should be awarded for a cancer missed by screening mammography  even if the cancer was missed as a consequence of the small failure rate of the test . Younger women living in metropolitan areas and women who had realistic expectations of the accuracy of the tests were more likely to favour financial compensation . CONCLUSION : Unrealistically high expectations of the sensitivity of screening mammography  were common in this group of women . Many women favoured financial compensation for missed cancers even if the cancer was missed solely because of the failure rate of the test . Public education is required to inform women of the limited sensitivity of breast cancer tests but this may not reduce cl aims for financial compensation when cancers are missed Expected utility theory is felt by its proponents to be a normative theory of decision making under uncertainty . The theory starts with some simple axioms that are held to be rules that any rational person would follow It can be shown that if one adheres to these axioms , a numerical quantity , generally referred to as utility , can be assigned to each possible outcome , with the preferred course of action being that which has the highest expected utility . One of these axioms , the independence principle , is controversial , and is frequently violated in experimental situations . Proponents of the theory hold that these violations are irrational The independence principle is simply an axiom dictating consistency among preferences , in that it dictates that a rational agent should hold a specified preference given another stated preference . When applied to preferences between lotteries , the independence principle can be demonstrated to be a rule that is followed only when preferences are formed in a particular way . The logic of expected utility theory is that this demonstration proves that preferences should be formed in this way An alternative interpretation is that this demonstrates that the independence principle is not a valid general rule of consistency , but in particular , is a rule that must be followed if one is to consistently apply the decision rule " choose the lottery that has the highest expected utility . " This decision rule must be justified on its own terms as a valid rule of rationality by demonstration that violation would lead to decisions that conflict with the decision maker 's goals This rule does not appear to be suitable for medical decisions because often these are one-time decisions in which expectation , a long-run property of a r and om variable , would not seem to be applicable . This is particularly true for those decisions involving a non-trivial risk of death Key words . expected utility theory , von Neumann-Morgenstern utility , strength of preference ; decision analysis ; independence principle . ( Med Decis Making 1996;16:1 - 6 The effectiveness and costs of prenatal screening programmes for Down 's syndrome using maternal serum markers will vary significantly depending on the biological cut-off values chosen in order to select women , at each maternal age , who will be sent for amniocentesis .  On the basis of the first French prospect i ve study of human chorionic gonadotropin ( hCG ) measurement in maternal serum , this paper shows that the screening protocol currently used in France , where hCG cut-off values are defined in order to offer amniocentesis to women of all ages with a 1 per cent fetal risk of Down 's syndrome , would detect 64.06 per cent of all cases of trisomy 21 at birth and would be highly profitable for the French social security system . On the basis of a representative sample of 100,000 pregnant women , the total costs of screening would reach $ 8,302,000 but would generate net potential savings of $ 32,186,000 in terms of life-long costs of care for trisomic 21 children which would be ' avoided ' by termination of pregnancy following a positive diagnosis of Down 's syndrome . Economic assessment shows that cost-benefit analysis would justify lower hCG cut-off values and a higher detection rate of fetal Down 's syndrome ( 74.45 per cent ) than the current French protocol . This paper concludes that it is ethical and value-laden issues , such as the consequences for women and couples of false positives and false negatives of screening , rather than economic and financial arguments that may set limits to the utilization of screening for Down 's syndrome using maternal serum markers like hCG During a prospect i ve study of the natural history of AIDS , 1001 homosexual or bisexual men were offered the opportunity to learn their HIV antibody status . Six hundred and seventy ( 67 % ) of the population who elected to do so were similar to the 331 ( 33 % ) people who declined in a number of baseline characteristics . All were counselled to practice safe sex . To determine whether disclosure of HIV serologic status affects subsequent sexual behavior , we examined changes at four time-points in three sexual activities during the previous 6 months : the number of male partners with whom the participant had ( 1 ) sexual intercourse , ( 2 ) unprotected anal receptive intercourse , and ( 3 ) unprotected anal insertive intercourse . All activities decreased strikingly over the 18-month study period . Following disclosure , the mean number of partners dropped to 47 % of the baseline number in people remaining unaware of their antibody status , to 45 % in people told that they were seropositive , and to 55 % in people told that they were seronegative . The mean number of partners for younger seropositives declined less than that for older seropositives . The mean number of partners with whom unprotected anal receptive intercourse was practice d declined to 57 % of baseline in unaware people , 42 % in aware seropositives , and 62 % in aware seronegatives . The mean number of partners with whom unprotected anal insertive intercourse was practice d declined to 52 % of baseline in unaware people , 42 % in aware seropositives and 59 % in aware seronegatives . Disclosure of a negative test result led to a significantly smaller decline in these sexual activities . ( ABSTRACT TRUNCATED AT 250 WORDS Abstract Objectives : To assess the experiences of obstetricians in Engl and and Wales of serum screening for Down 's syndrome . Design : Postal question naire survey . Subjects : Question naires were sent to all practising obstetricians in Engl and and Wales with non-academic20appointments who had not participated in an earlier ( r and omly sample d ) survey of obstetricians ' attitudes ( n=555 ) . Responses were received from 393 ( 71 % ) , of which 351 were analysed . The data represent about one third of obstetric consultants in Engl and and Wales . Main outcome measures : The extent of use of serum screening for Down 's syndrome , and the problems encountered . Results : Serum screening for Down 's syndrome was being offered on some basis by virtually all obstetricians in the survey . Nearly half the sample said that they did not have adequate re sources for counselling all the women to whom screening was offered . Many problems were reported , which in all cases were more common than equivalent problems encountered with serum screening for neural tube defects . Over 80 % ( 289 ) said that women not underst and ing the test was a problem . Conclusions : There is considerable confusion associated with serum screening for Down 's syndrome . The precedent of serum screening for neural tube defects does not seem to have lessened the problems experienced , rather the contrary . Many obstetricians report inadequate re sources for counselling , which is consistent with the high prevalence of problems associated with women not underst and ing the test . There is an urgent need to consider what counselling should consist of and who should undertake it and to ensure that necessary re sources are available We performed two studies using only written and video material s to educate people about cystic fibrosis ( CF ) and carrier screening . Participants were r and omized to receive  written or video material s. All received a brief question naire . Subjects in group I ( n = 238 ) were ( 1 ) individuals in steady relationships and their partners , ( 2 ) > or = 18 years old , and ( 3 ) not pregnant . Those who accepted free screening and were not demonstrable carriers were sent a letter explaining their results and another question naire . Subjects in group II ( n = 108 ) were parents seeking well child care in a university clinic . The main outcome measures were ability to answer questions correctly about ( 1 ) health status of CF carriers and people with CF , ( 2 ) the possibility of false-negative results , and ( 3 ) for those who had screening , the implication s of their own results . Written and video material s were equally effective in conveying information . Prior to screening , subjects answered an average of 86 % of questions correctly . Subjects with less formal education answered fewer questions correctly ; 60 % of those with less than a high school education had adequate knowledge of the health consequences of having CF or being a carrier , compared with > or = 94 % of college graduates . Performance improved after screening . Where neither partner was a demonstrable carrier , 88 % knew their own and their partner 's test results , and 90 % indicated that their risk of having a child with CF was not zero . Written and video educational material s can be used without face-to-face counseling to inform most people about carrier screening and their test results . These material s may be less effective for those with lower educational background Objective To examine the prevalence and predictors of repeat  HIV testing .  Design , setting and participants Cross-sectional data from two r and om household- based and two bar-based sample s of gay/bisexual men in two medium-size cities ( Tucson , Arizona and Portl and , Oregon ) with substantial numbers of AIDS cases , in 1992 ( n = 2602 ) . Main outcome measureThe prevalence and predictors of repeat testing  among men who reported being HIV-tested at least once but not being HIV-positive ( n = 1583 ) . Results In total , 51 % of the sample had been tested three or more times , and 15 % were tested more than once every 6 months . Men with higher risk were more likely to be repeatedly tested , although oral but not anal risk was a significant predictor of repeat testing in regression analyses . Men who did not know the HIV status of their primary partner were less likely to be repeatedly tested .  Men who perceived that social norms favored secondary prevention , specifically adherence to medical recommendations for the treatment of HIV infection , and who communicated more often about testing were more likely to be repeatedly tested . Conclusions Policy and clinical recommendations for repeat testing must be based on consideration of the complexity and multi-faceted nature of repeat testing . For some individuals , repeat testing may play a legitimate role in HIV prevention by reinforcing safe behavior and providing confirmation of HIV-negative status . However , for others repeat testing may indicate a need for different or more intensive interventions to encourage safe sex This study aim ed to determine factors that influence fecal occult blood test performance in colorectal cancer screening . A r and om sample was selected of men and women ages 50 to 74 years of age who had been mailed a fecal occult blood testing kit in a screening program in fall 1986 . One year after initial test mailing , sample group members ( n = 504 ) were surveyed by telephone . Four months later , the survey sample received a second fecal occult blood test mailing . Multivariable analysis for subjects with vali date d past fecal occult blood test status ( n = 322 ) revealed the past testing was positively associated with physician encouragement of screening , age , the belief that cancer is curable , perceived test efficacy , and strong intention to do testing . It also was discovered that persons who felt that they had little control over their health were more likely to have done past testing . Preliminary analysis 
    Output:
    
There is some evidence that false-negative results may have a large legal impact .
For example , in cervical screening they have led to legal action and its associated costs , including payment of compensation ; this is based on reports of events in both the UK and US health systems .
False-negatives are evident in all screening programmes , even when the quality of the service provided is high .
They may have the potential to delay the detection of breast and cervical cancer , but there is little evidence to help assess their psychological consequences in these or other screening programmes .