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Per-Henrik Zahl

Publications and source records attributed to Per-Henrik Zahl.

18 recordsLinked to original sources
PubMed2006

Results of the Two-County trial of mammography screening are not compatible with contemporaneous official Swedish breast cancer statistics.

BACKGROUND: National mammography screening programmes are based on the results of randomised trials, but the quality of these trials has recently been questioned. The Swedish Two-County trial reported a 31% reduction in breast cancer mortality and was instrumental for the introduction of screening in many countries. In this trial, official Swedish health registries were used to identify breast cancers and breast cancer deaths in the study population. METHODS: We used data from the same registries to estimate the numbers of breast cancer cases and breast cancer deaths among the included women. RESULTS: Compared to official Swedish statistics we found that 192 breast cancer cases and 43 breast cancer deaths seem to be missing in the main publication of the Two-County trial; we found similar discrepancies in two updates of the trial. These large differences can hardly be explained by random fluctuations in the cancer occurrence. CONCLUSION: The data reported for the Two-County trial are incomplete. Other data indicate that the mortality results in a recent report were flawed.

Bias↗
PubMed2005

Is birth history the key to highly educated women's higher breast cancer mortality? A follow-up study of 500,000 women aged 35-54.

A positive relationship has been found between high levels of education and breast cancer mortality. The aim of our study is to determine if the educational gradient in breast cancer mortality persists after adjustment for reproductive history. Register data including the total adult population in Norway were used. A total of 512,353 Norwegian women 35-54 years of age at the Norwegian Census in 1990 were followed with respect to breast cancer deaths until December 31, 2001. The analysis included 2,052 breast cancer deaths in 5.6 million person years. Educational differences in breast cancer mortality were analysed using Cox regression. The age adjusted relative risk of dying from breast cancer for women with >12 years of education compared to women with <10 years was 1.25 (95% confidence limits [CI] = 1.10-1.41). Adjustment for age at first birth with nulliparous as reference category reduced this difference to 1.08 (95% CI = 0.95-1.23). For parous women, age at first birth explained all the educational difference in breast cancer mortality. Among nulliparous women there was a larger positive educational gradient in breast cancer mortality than among parous women (relative risk [RR] = 1.57, 95% CI = 1.15-2.13), indicating that there were differences in other confounders than birth history among the childless.

Adult↗
PubMed2005

Social inequalities in mortality: changes in the relative importance of income, education and household size over a 27-year period.

BACKGROUND: The aim of this paper was to measure socio-economic inequalities in mortality over a 27-year period, and estimate the simultaneous effects of education and income adjusted for changing proportions and potential confounders. METHODS: Census data in 1970, 1980 and 1990 with information about income, educational level and household size were linked to mortality records at the individual level and analysed with absolute mortality rates, Poisson regression (univariate and multivariate) and Relative Index of Inequality (RII). RESULTS: Mortality differences increased between income quartiles and educational groups as well as between singles and non-singles. RII between income quartiles increased from 1.6 to 3.6 for men and 1.7 to 2.7 for women while RII between the educational groups increased from 1.6 to 2.8 for men and 1.5 to 2.1 for women. However, RII derived from the adjusted multivariate regression analysis was 1.8 (men) and 1.9 (women) between the income groups in 1990 and 2.2 (men) and 1.7 (women) between the educational groups. In the 1990s current income was more important than previous income, and the rate ratios (RR) increased for groups dropping into the lowest income quartile between two censuses. CONCLUSION: Low education and single status have become relatively more important risk factors for mortality over time. Confounder effects of education and household size could partly explain the seemingly large increase in inequalities between income groups. Results may also indicate a stronger reverse causation (poor health causing low income) over time.

Censuses↗
PubMed2004

[Overdiagnosis in mammography screening].

BACKGROUND: In Norway and Sweden, the introduction of mammography screening programmes has been associated with about a 50% increase in breast cancer incidence for the screened age groups and almost stable incidence in higher age groups. This suggests that mammography screening results in a substantial degree of overdiagnosis. MATERIAL AND METHODS: In a prospective cohort study of the Norwegian mammography programme we recorded the incidence of breast cancer among women aged 50 to 69 years offered mammography screening as well as the incidence of interval cancer among those attending, and breast cancer among those not attending. We used these data to calculate the incidence of cancer detected by screening among those screened. RESULTS: The incidence of invasive cancer at second and third screening is 2.4 times higher than expected. We estimated that only 42% of the screening-detected invasive cancers would have developed into clinical disease in the absence of a screening programme. When ductal carcinoma in situ is added, only 34% of the screening-detected cancers would have developed into clinical disease. INTERPRETATION: Two thirds of breast cancers detected by screening are overdiagnosed.

Aged↗
PubMed2004

Incidence of breast cancer in Norway and Sweden during introduction of nationwide screening: prospective cohort study.

OBJECTIVE: To determine whether any increase in the incidence of breast cancer in women detected by mammography is compensated for by a drop in the incidence after age 69, years when women are no longer invited for screening. DESIGN: Population based cohort study of incidence of breast cancer during the introduction of nationwide screening programmes. SETTING: Norway and Sweden. PARTICIPANTS: All women aged above 30 years (1.4 and 2.9 million, respectively, in 2000). MAIN OUTCOME MEASURES: Changes in age specific incidence rates of invasive breast cancer associated with the introduction of the screening programmes. RESULTS: As a result of screening the recorded incidence of breast cancer in women aged 50-69 years increased by 54% in Norway and 45% in Sweden. There was no corresponding decline in incidence after the age of 69 years. CONCLUSIONS: Without screening one third of all invasive breast cancers in the age group 50-69 years would not have been detected in the patients' lifetime. This level of overdiagnosis is larger than previously reported.

Adult↗
PubMed2003

[Social inequality and trends in mortality among singles in Norway].

BACKGROUND: Mortality rates are known to be high among singles, a group that has increased over time. Monitoring the health status of singles and identifying high-risk subgroups are valuable efforts for evaluation and planning purposes. MATERIAL AND METHODS: Information about household size, income, education and sex among all Norwegians aged 45-59 and 60-69 in 1970, 1980 and 1990 has been linked to mortality data from 1970-77, 1980-87 and 1990-97. RESULTS: In the age group 45-59, mortality rates was down by 4 per cent among single men and up by 11 per cent among single women from the 1970s to the 1990s, while mortality rates went down by 38 % among non-single men and 22 % among non-single women. Differences in mortality between singles and others have increased over time for the 45-59 age group, but not for the 60-69 age group. Social inequalities in health are larger among singles. INTERPRETATION: In the age group 45-59, single households represent an increasing public health problem. A weakened relative financial position and more singles being divorced are factors of possible significance.

Adult↗
PubMed2003

Regression analysis with multiplicative and time-varying additive regression coefficients with examples from breast and colon cancer.

Regression analysis may be used to simplify the representation of mortality rates when there are many significant prognostic covariates or to adjust for confounding effects. The principal request of the regression model in this range of use is to have unbiased parameter estimates. A model with constant multiplicative and time-varying additive regression coefficients is discussed. The model allows some covariate effects to be multiplicative while allowing others to have a time-varying additive effect. Thus, it is a mix of classical Cox regression and Aalen's additive risk model. A major characteristic of cancer mortality rates, in contrast to general mortality rates, is that hazard rates, after a potentially initial increase, decrease, although not always tending to zero. Cancer diseases, like breast and colon cancer, have significantly increased cause-specific mortality rates even 20 years after diagnosis. Another major feature in cancer survival analysis is that many covariate effects are time-varying. Some covariate effects, like age at diagnosis, may only be significant for a limited time after diagnosis. Furthermore, some treatment procedures may initially decrease the mortality, while the long-term effect may be opposite. A third issue is that average covariate effects are very often not multiplicative. Estimation is carried out iteratively; the cumulative additive regression functions are estimated non-parametrically using a least-squares method and the multiplicative parameters are estimated from the partial likelihood. The method is applied on 3201 female breast cancer and 1372 male colon cancer patients.

Adult↗