Statistical analysis of survey-based event history data with application to modeling of unemployment duration

Longitudinal surveys are increasingly used to collect event history data on person-specific processes such as transitions between labour market states. Surveybased event history data pose a number of challenges for statistical analysis. These challenges include survey errors due to sampling, non-response, attrition and measurement. This study deals with non-response, attrition and measurement errors in event history data and the bias caused by them in event history analysis. The study also discusses some choices faced by a researcher using longitudinal survey data for event history analysis and demonstrates their effects. These choices include, whether a design-based or a model-based approach is taken, which subset of data to use and, if a design-based approach is taken, which weights to use. The study takes advantage of the possibility to use combined longitudinal survey register data. The Finnish subset of European Community Household Panel (FI ECHP) survey for waves 1–5 were linked at person-level with longitudinal register data. Unemployment spells were used as study variables of interest. Lastly, a simulation study was conducted in order to assess the statistical properties of the Inverse Probability of Censoring Weighting (IPCW) method in a survey data context. The study shows how combined longitudinal survey register data can be used to analyse and compare the non-response and attrition processes, test the missingness mechanism type and estimate the size of bias due to non-response and attrition. In our empirical analysis, initial non-response turned out to be a more important source of bias than attrition. Reported unemployment spells were subject to seam effects, omissions, and, to a lesser extent, overreporting. The use of proxy interviews tended to cause spell omissions. An often-ignored phenomenon classification error in reported spell outcomes, was also found in the data. Neither the Missing At Random (MAR) assumption about non-response and attrition mechanisms, nor the classical assumptions about measurement errors, turned out to be valid. Both measurement errors in spell durations and spell outcomes were found to cause bias in estimates from event history models. Low measurement accuracy affected the estimates of baseline hazard most. The design-based estimates based on data from respondents to all waves of interest and weighted by the last wave weights displayed the largest bias. Using all the available data, including the spells by attriters until the time of attrition, helped to reduce attrition bias. Lastly, the simulation study showed that the IPCW correction to design weights reduces bias due to dependent censoring in design-based Kaplan-Meier and Cox proportional hazard model estimators. The study discusses implications of the results for survey organisations collecting event history data, researchers using surveys for event history analysis, and researchers who develop methods to correct for non-sampling biases in event history data.

Securin, Cdc20 and Cdc27 in predicting the outcome of human breast cancer

Deregulated proliferation has been recognized among the most important factors promoting breast cancer development and progression. The aim of the project is to gain understanding of the role of specific cell cycle regulators of metaphase-anaphase transition and evaluate their potential in breast cancer prognostication and treatment decisions. Metaphase-anaphase transition is triggered by activation of anaphase promoting complex (APC) which is activated by a cascade of regulatory proteins, among them securin, Cdc20 and Cdc27. These proteins promote the metaphase–anaphase transition and participate in the timely separation of the chromatids. This study is based on a patient material of approximately 600 breast cancer patients and up to 22 years of follow-up. As the main observation, based on DNA cytometric and immunohistochemical methods, securin, Cdc20 and Cdc27 protein expressions were associated with abnormal DNA content and outcome of breast cancer. In the studied patient material, high securin expression alone and in combination with Cdc20 and Cdc27 predicted up to 9.8-fold odds for aneuploid DNA content in human breast cancer. In Kaplan–Meier analyses, high expression of securin systematically indicated decrease in breast cancer survival as compared to low expression cases. The adverse effect of high securin expression was further strengthened by combining it with Cdc20 or Cdc27 expressions, resulting in up to 6.8-fold risk of breast cancer death. High securin and Cdc20 expression was also associated with triple-negative breast cancer type with high statistical significance. Securin, Cdc20 or Cdc27 have not previously been investigated in a clinically relevant large breast cancer patient material or in association with DNA ploidy. The present findings suggest that the studied proteins may serve as potential biomarkers for identification of aggressive course of disease and unfavourable outcome of human breast cancer, and that they may provide a future research aim for understanding abnormal proliferation in malignant disease.

Elinaikamallit silmänliiketutkimuksessa

Silmänliiketutkimus on hieman yli 100 vuotta sitten alkunsa saanut tutkimusmenetelmä, jossa silmänliikkeitä seuraamalla saadaan tietoa siitä, mihin ihmisen katse kiinnittyy kuvaa katsoessa tai tekstiä lukiessa. Silmänliikkeiden mittaamiseen käytetään silmänliikekameroita, joiden avulla katseen liikkeistä voidaan erotella katseen siirtymiset eli sakkadit, sekä fiksaatiot, jotka ovat pysähtymisiä näiden siirtymien välillä. Tässä tutkielmassa sovelletaan elinaikamalleja Turun yliopiston psykologian laitoksella kerättyyn silmänliikeaineistoon, jossa on tutkittu koehenkilöiden silmänliikkeitä heidän lukiessaan erityyppisiä väittämiä. Tutkielmassa selvitetään elinaika-analyysin menetelmin, miten lukijan oma asenne vaikuttaa lukenemisprosessiin, ja miten katseen eteneminen eroaa erityyppisissä virkkeissä. Tutkittavina silmänliikemuuttujina on sanojen ensilukuaika sekä virkkeen kokonaislukuaika, ja virkkeiden aiheena on maahanmuutto. Eri asenneryhmien jakaumia tarkastellaan Kaplan-Meier -estimaateilla, ja asenteen vaikutusta erityyppisten virkkeiden lukemiseen tutkitaan semiparametrisella Coxin mallilla. Lukijan asenteella ei voitu todeta olevan vaikutusta sanojen ensilukuaikaan, eli asenteella ei ollut vaikutusta katseen etenemiseen virkkeiden ensimmäisellä lukukerralla. Virkkeiden kokonaislukuajoissa havaittiin selvästi enemmän vaihtelua, mutta erot olivat samansuuntaisia kaikissa virketyypeissä. Negatiivisen asenteen omaavilla lukijoilla kokonaislukuajat olivat pidempiä virkkeen tyypistä riippumatta, mutta suurimmat erot asenneryhmien välillä havaittiin luettaessa positiivisia virkkeitä. Negatiivisen suhtautumisen luettavaan aiheeseen voidaan siis sanoa hidastavan lukemisprosessia.

Julius Meier-Graefe kaksissa kansissa

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