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PubMed1991

Construction of expanded continuous life tables--a generalization of abridged and complete life tables.

This article extends the recent abridged life-table method of Hsieh. It generalizes the conventional discrete (abridged and complete) life tables into a continuous life table that can produce life-table functions at any age and develops a unified method of life-table construction that simplifies the disparate laborious procedures used in the traditional approach of constructing abridged and complete life tables. A set of precise procedures based on the complete cubic spline for the main body of the table and a mortality law for advanced ages is developed for estimating the basic and nonbasic life-table functions from a given mortality schedule. The proposed method can also produce more life-table functions than other existing methods. The method is illustrated with Canadian data.

Humans↗
PubMed1976

Calculation of survival rates by the life table and other methods.

The last few years have seen the introduction of medical statistics into the curriculum for MB, BS and for the FFR. Also, an increasing number of clinical trials have considered statistics at the planning stage of the trial, rather than only at the end point. However, there is one particular aspect of medical statistics which has consistently been neglected, namely, technique in calculating survival rates for cancer patients. All too often, a direct method of calculation, see section 3.1, is used when a life table method would provide a better estimate. The life table, or actuarial method, was first described in a medical context by Greenwood (1926), and later by Merrell and Shulman (1955) and Cutler and Ederer (1958). It has however, not been explained in detail in a British journal. The objective of the present paper is to remedy, this fact so that it can be used more widely in the future in preference to a direct method.

Humans↗
PubMed1991

Recurrence rates of treated basal cell carcinomas. Part 1: Overview.

This is the first article in a series reviewing the extensive experience of the Oncology Section of the Skin and Cancer Unit, from 1955 through 1982, with 5755 basal cell carcinomas (BCCs) treated by curettage-electrodesiccation, surgical excision, or x-ray therapy. Recurrence rates were calculated by three methods for each of the treatment modalities: 1) by the raw recurrence rate method; 2) by the "strict" 5-year recurrence rate method; and 3) by modification of the life-table method. Our analyses show that the last method best approximates the true recurrence rate. Primary (previously untreated) BCCs had a 5-year recurrence rate of 10.6% (standard error 0.6%), and previously treated BCCs had a rate of 15.4% (standard error 1.3%) (P = .0002). The greatest risk for recurrence of treated primary BCCs occurred 1 to 4 years after therapy. It is concluded that recurrence rates of primary BCCs should be reported separately from those of previously treated BCCs and that the modified life-table method is best suited to calculate 5-year recurrence rates.

Adolescent↗
PubMed1978

[Problems in the evaluation of contraceptives (author's transl)].

For the evaluation of the effectiveness of contraceptives the Life Table method is at present the best method. It is a disadvantage that the original method of Tietze & Potter was restricted to the evaluation of intra-uterine contraception devices. A Belgian team is now in the process of developing a modified life table method for the evaluation of the effectiveness and the side effects of oral contraceptives. The reference to the Pearl-index for the effectiveness of contraceptives is unclear and in the way in which it is at present used scientifically untenable.

Clinical Trials as Topic↗
PubMed2001

Prevalence corrected hysterectomy rates and probabilities in Utah.

PURPOSE: A life table method is used for correcting hysterectomy rates and probabilities for prevalent cases of hysterectomies in the population. Both corrected and conventional hysterectomy rates and probabilities are reported. METHODS: Hysterectomy prevalence estimates are derived from cross-sectional hysterectomy and mortality using a life table method. Analysis is based on the Utah Hospital Discharge Data Base and State death certificates. RESULTS: Hysterectomy rates are strongly influenced by age, reaching 150 per 10,000 for ages 45-49 years. The corresponding corrected hysterectomy rate is 196. Differences between the corrected and uncorrected cause-specific hysterectomy rates tend to be most pronounced at their peaks, particularly later in life where the prevalence of hysterectomy is greatest. Probability of hysterectomy approaches slightly above 35% over the life span, whereas the corrected hysterectomy probability approaches 43%. Probability of hysterectomy in the next 10 years is 12.9% for women aged 35 years and 11.7% for women aged 45 years. Corresponding corrected hysterectomy probabilities are 14.3 and 15.1. Higher prevalence of hysterectomy in later ages explains the reverse in magnitude of the rates when the correction is applied to the hysterectomy rates. CONCLUSIONS: Conventional hysterectomy rates are underestimated, particularly in older age groups. A prevalence correction of the rates and probabilities is necessary to fully understand the potential health related consequences and impact of this medical procedure in the population.

Adult↗
PubMed1986

A modified actuarial life-table approach to the analysis of implantable device performance.

The actuarial life-table method is often used by pacemaker manufacturers and the pacing research community to describe pacemaker and lead performance. Most life-table methods allow for differing lengths of follow-up but assume that all devices were followed from implant. Occasionally, however, devices come under follow-up observation sometime after implant. This presentation describes an extension of the actuarial method to accommodate these kinds of data. The specific example to be considered involves follow-up data collected by CardioCare, a commercial cardiac monitoring service, on the performance of Medtronic polyurethane leads. Patients subscribe to this service, generally at some time after actual device implant. Results showed that of 12,112 patients with Models 4002, 6971, and 6972 leads who were followed by CardioCare, only 85 were followed from implant. If one were to exclude patients not followed since implant, more than 99% of the data would be lost. Using the modified approach with allowance for postimplant, entry resulted in an estimated three-year cumulative survival probability for these leads of 95.7%. Treating all patients as if they were followed since implant, the probability would be 96.9%, an optimistic and biased estimate.

Actuarial Analysis↗
PubMedDate not supplied

The effectiveness of lithium prophylaxis in bipolar and unipolar depressions and schizo-affective disorders.

The effectiveness of lithium prophylaxis in bipolar affective disorders is generally supported in the literature. The effects in this group, as well as in unipolar depressions and schizo-affective disorders were studied, using an individual retrospective control method, and the Life Table method. Lithium prophylaxis resulted in a substantial decrease in the number of episodes and hospital admissions in bipolar and schizo-affective disorders. In addition, these two groups showed frequent relapses after termination of the prophylaxis. The number of episodes preceding the prophylaxis and the absence of unipolar depression are found to be predictors of effectiveness. The consequences of patient selection and of inconclusive diagnostic criteria are pointed out.

Adult↗
PubMed1976

Optic neuritis in relation to multiple sclerosis.

Available estimates of the frequency with which a patient with optic neuritis develops multiple sclerosis range from as low as 13% to as high as 87%. In an effort to obtain a better estimate, a nation-wide study of optic neuritis was carried out in Israel. Patients who fulfilled strict diagnostic criteria of optic neuritis were identified and examined periodically. Between 1955 and 1964, 105 patients were found and on the basis of these, the average annual age-adjusted incidence of optic neuritis in Israel was 0.56 per 10(5) population compared to 1.2 per 10(5) cases of multiple sclerosis per year, i.e. optic neuritis was about half as frequent as multiple sclerosis each year. As with multiple sclerosis, optic neuritis was more common in European immigrants to Israel than Afro-Asian immigrants. During a follow-up interval which ranged from 3.3 to 15.6 years (mean 9.5 years), at least 27 of the 105 patients developed multiple sclerosis (28%). A life-table analysis showed that after 10 years 32.3 +/- 5.6% of patients with optic neuritis would develop multiple sclerosis and, after 14 years, about half would develop multiple sclerosis. Risk of dissemination was highest in those who were youngest when optic neuritis developed. Neither sex nor ethnic background influenced risk significantly. Results of the present study support earlier work using life-table methods carried out in Hawaii which also showed that between 29 and 39% of patients with optic neuritis will develop multiple sclerosis within 10 years of onset. The life-table method is a better predictor of prognosis than newer laboratory techniques such as spinal fluid studies of IgG, kappa-lambda light chain ratios and serum/CSF IgG ratios.

Adolescent↗
PubMed1982

[Statistical methods in the evaluation of the therapeutic efficacy--their problems and solutions].

In order to evaluate the therapeutic efficacy accurately, it is necessary to conduct a well-designed clinical trial and to draw conclusions after considering both the statistical significance and the clinical significance. The well-designed clinical trial needs to meet at least the following three conditions: (1) the acquisition of the minimal sample size to obtain statistically significant results, (2) the existence of an adequate control (standard) treatment group, and (3) the good comparability between treatment groups. In order to secure the good comparability between treatment groups, it is desirable to conduct a stratified randomized controlled clinical trial in the form of a multi-clinic cooperative study in case it is difficult to secure the enough sample size in one institute. The concept and problems of the life table methods which are frequently used in the clinical trial were discussed. The merits and limitations of the multivariate analyses, especially the Cox multiple regression life table method, were also discussed in this paper.

Analysis of Variance↗
PubMed1986

Hepatitis-free interval after clotting factor therapy in first infused haemophiliacs.

Post-infusion hepatitis is known to occur very frequently in haemophiliacs after treatment with unheated commercial clotting factor concentrates, obtained from large plasma donation pool. On the contrary, single-donor cryoprecipitate is likely to carry a lower risk of transmitting hepatitis. To evaluate this hypothesis, we retrospectively reviewed the medical records of 25 first infused haemophiliacs (from 1981 to 1984) treated with unheated commercial clotting factor concentrates (n = 19) or cryoprecipitate (n = 6). The hepatitis-free interval after the beginning of therapy was expressed as exposure days. The end point of each patient, i.e. the hepatitis occurrence, was defined as an increase of amino-transferases (ALT and AST) and/or the seroconversion of HBV-markers, which were checked every three months. The life-table method and log-rank test showed that cryoprecipitates had a significantly longer hepatitis-free interval (p = 0.0131, log-rank test) and a lower risk of transmitting hepatitis (p = 0.01-0.05, life-table method) than the commercial concentrates. However, the safety of cryoprecipitate therapy was shown to cover only a few exposure days, and so the real advantage of this product depends on the bleeding frequency of the patient concerned. We believe that these methods and our findings may be useful to assess and compare the safety of the new "heat-treated" clotting factor concentrates.

Adolescent↗
PubMed1979

The impact of heterogeneity in individual frailty on the dynamics of mortality.

Life table methods are developed for populations whose members differ in their endowment for longevity. Unlike standard methods, which ignore such heterogeneity, these methods use different calculations to construct cohort, period, and individual life tables. The results imply that standard methods overestimate current life expectancy and potential gains in life expectancy from health and safety interventions, while underestimating rates of individual aging, past progress in reducing mortality, and mortality differentials between pairs of populations. Calculations based on Swedish mortality data suggest that these errors may be important, especially in old age.

Actuarial Analysis↗
PubMed1994

Long-term risk of IDDM in first-degree relatives of patients with IDDM.

Due to a short observation period previous studies may have underestimated prevalence and recurrence risk of IDDM in relatives of IDDM patients. To obtain a more exact life-time risk estimate we identified 310 probands, representative of Danish IDDM patients, characterized by current age more than 50 years, age at onset 40 years or less and diabetes duration of more than 30 years. Family data were obtained from 291 probands. Mean "observation" times (age) (+/- SD) for siblings (n = 553) and offspring (n = 359) were 59.4 +/- 16.1 years and 33.8 +/- 8.8 years, respectively. Of the probands 73 (25.1%) had at least one first-degree relative with IDDM. Seventeen percent had at least one affected sibling. An increase from 10.4% to 22.4% of having first-degree relatives with IDDM among probands with age at onset below 20 years was observed during the period from proband at age 21 years up to 1 September 1992. Among affected siblings 48% of the second cases were affected more than 10 years after the first affected sibling. Using the life-table method cumulative recurrence risks from time of birth were calculated for siblings up to age 30 years of 6.4% and up to age 60 years of 9.6%. For offspring the risk up to age 34 years was 6.3%. In addition, we present a life-table method evaluating the cumulative recurrence risk from time of onset in the proband, as this is the most relevant when giving genetic counselling. In conclusion, the long-term risks of IDDM in siblings and offspring are high compared to that shown in previous reports.

Aged↗
PubMed1992

Predictors of relapse in peptic ulcer.

Four hundred and two patients with peptic ulcer were selected for acute therapy with either pirenzepine (100 mg/day) or cimetidine (800 mg/day) using the envelope method. Those who achieved healing within 3 months (251 patients) were randomized in a double-blind fashion to maintenance therapy with either pirenzepine (75 mg/day) or placebo. In a preliminary study of 163 patients in which a multiple regression life-table method was employed, 4 out of 15 possible predictors were found to have a significant influence on relapse. These were site of ulcer lesions, psychological stress, endoscopic findings at the time of healing of the original ulcers, and acute therapy. Stratified analysis of the evolution of relapse by the Cutler-Ederer life-table method indicated that several other factors also influenced relapse in certain patient subgroups. Most relapses (93.8%) occurred at the same site as, or close to the site of, the original ulcers, indicating that ulcer scars also play a role in relapse.

Adult↗
PubMed1986

Univariate and multivariate analyses of cadaver kidney graft survival data.

1. Clinical data on 6632 first cadaver transplants performed since January 1983 were analyzed by multivariate (Cox regression) and univariate (life-table) methods. 2. Cox regression analysis showed blood transfusion, recipient's race, HLA mismatch, highest antibody, warm ischemia time, and cyclosporine treatment as significant factors affecting graft survival. 3. A comparison of survival curves predicted by Cox regression analysis and that by the life-table method showed close agreement between the two methods. 4. Cyclosporine was one of the most significant variables affecting graft survival. There was a 13% overall increase in one-year graft survival due to cyclosporine treatment. However, other factors were still significant; they have not become obsolete in the cyclosporine era.

Cyclosporins↗
PubMed1995

[20 years orthograde venous bypass for infrainguinal arterial reconstruction].

During a 20-year period (1973-1993) a series of 684 orthograde vein bypass procedures with the translocated greater (or lesser) saphenous vein was performed in 629 patients (422 male, 207 female) of whom 221 (35%) were diabetics. There were 499 femoro-popliteal grafts to the infrageniculate popliteal artery, 158 femoro-crural and 27 popliteo-crural grafts. Indication for surgery was rest pain and/or tissue necrosis in 404, claudication in 277 and asymptomatic popliteal artery aneurysm in 3 extremities. All patients received long-term oral anticoagulation and were followed at regular intervals. At the concluding follow-up (01-06/1993) graft function was investigated by colour flow duplex scanning and/or arteriography. Cumulative patient survival at 1, 5, 10 and 15 years was 90.6%, 62.8%, 38.6% and 27.1%. Multivariate analysis (Cox-model) proved that preoperative clinical status (rest pain and tissue necrosis vs. claudication and asymptomatic popliteal artery aneurysm) (p < 0.0001) and diabetes (p < 0.001) were significant factors for survival. The 30-day patency rate was 93%, and the secondary cumulative patency rates (life-table method) were 85.7%, 78.6%, 73.8% and 65.9% at 1, 5, 10 and 15 years. Only the preoperative clinical status was a weak prognostic factor (Mantel p < 0.029) whereas diabetes or the level of proximal and distal anastomosis were without importance for graft performance. Cumulative limb salvage rates (life-table method) at 1, 5, 10 and 15 years were 91.2%, 85.6%, 83.4% and 79.9% for the 404 legs operated for rest pain and or necrosis; and they were 100%, 98.8%, 97.7% and 94.9% for the 277 legs with claudication.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed2001

The durability of endoscopic saphenous vein grafts: a 5-year observational study.

BACKGROUND: Endoscopic saphenous vein harvest has been explored as a minimally invasive alternative to a long continuous leg incision for removal of the greater saphenous vein. The endoscopic technique uses limited incisions (2-4) with extended "skin bridges" and videoscopic equipment for the dissection and removal of the greater saphenous vein. This study was undertaken to evaluate the long-term durability of saphenous vein grafts harvested by an endoscopic technique and used for lower extremity arterial revascularization. METHODS: All patients who underwent endoscopic saphenous vein harvesting for lower extremity arterial bypass grafting were prospectively followed for graft patency and risk factors. Grafts were surveyed with serial duplex scans at 3- to 6-month intervals over this 5-year study. Life-table methods were used to assess graft survival. A computerized registry and medical records were reviewed to determine graft patency and patient survival. RESULTS: From September 1994 to August 2000, 164 lower extremity arterial saphenous vein grafts harvested by an endoscopic technique were used for lower extremity arterial bypass grafting in 150 patients. The patient population included 111 males (75%) and 112 smokers (75%), but also included a high-risk cohort of 65 diabetic patients (43%) and 15 patients undergoing dialysis/renal transplant (10%). Twenty-eight patients (19%) died within the study period. With life-table methods, 1-, 3-, and 5-year secondary patency rates were 85% (+/- 3.2%), 74% (+/- 5.7%), and 68% (+/- 11.6%). Of the 30 failed grafts, 7 (4%) failed in the first month related to inadequate runoff (4), cardiac instability (2), and an additional surgical procedure (1). Twenty-three grafts (14%) failed between 1 and 42 months. Twenty-two (16%) of these 134 patent grafts underwent a second procedure to maintain patency (13 as primary-assisted patency and 9 as secondary patency). CONCLUSIONS: Endoscopic saphenous vein harvest for lower extremity arterial reconstruction provides a satisfactory conduit for lower extremity bypass grafting. Although increased manipulation from this limited access technique may incite an injury response in the vein, these vein grafts can maintain an adequate patency for lower extremity bypass grafting.

Adult↗
PubMed1986

Corneal graft survival: a retrospective Australian study.

Four hundred and forty-eight consecutive corneal grafts are analysed and their survival calculated using the actuarial life-table method. Overall survival at two years is 81 +/- 4% and at five years is 65 +/- 5%. Within diagnostic subgroups keratoconus has the best prognosis. Previous graft failure and recipient corneal vascularization are shown to have a negative effect on graft survival. Sex of patient, urgency of operation and use of combined procedures do not affect survival and second regrafts fare no worse than first regrafts. The use of the actuarial life-table method of analysing graft survival is discussed and its importance emphasized.

Actuarial Analysis↗
PubMed1997

Results of a pilot study of the time to azoospermia after vasectomy in Mexico City.

In a joint pilot study by Family Health International (FHI), AVSC International, and the Instituto Mexicano del Seguro Social (IMSS), information was gathered on the determinants of azoospermia following vasectomy on 38 healthy men who chose vasectomy for contraception. The time and number of ejaculations associated with loss of sperm motility and loss of sperm eosin vital staining were also evaluated. "Azoospermia" was defined on the basis of two consecutive azoospermic semen samples collected at least 3 days apart. The single decrement life table method was used to calculate weekly gross cumulative life table rates for the time to azoospermia, zero motility, and zero viability. The Kaplan-Meier method was used to calculate the product-limit estimates of the cumulative rates for the total number of ejaculations to azoospermia, 0% motility and 0% viability. The median time to azoospermia was 10 weeks and at the end of week 20, the life table rate (+/- standard error) was 93.0 (+/- 6.30) weeks/100 men. The median number of ejaculations to azoospermia was between 25 and 30, and the cumulative rate (+/- standard error) at 60 ejaculations reached 94.5 (+/- 5.16)/100 men.

Adult↗