• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 22
  • 21
  • 1
  • Tagged with
  • 22
  • 22
  • 22
  • 22
  • 11
  • 10
  • 10
  • 9
  • 8
  • 8
  • 6
  • 6
  • 5
  • 5
  • 5
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

模糊隨機變數在線性迴歸模式上的應用 / Fuzzy Random Variables and Its Applications in Fuzzy Regression Model

曾能芳 Unknown Date (has links)
傳統迴歸分析是假設觀測值的不確定性來自於隨機現象,本文則應用模糊隨機變數概念於迴歸模式的架構,考慮將隨機現象和模糊認知並列研究。針對樣本模糊數(x<sub>i</sub>, Y<sub>i</sub>),我們進行模糊迴歸參數估計,並稱此為模糊迴歸模式分析。模糊迴歸參數估計大都採用線性規劃,求出適當區間,將觀測模糊數Y<sub>i</sub>的分佈範圍全部覆蓋。但是此結果並不能充分反映觀測樣本Y<sub>i</sub>的特性。本研究提出一套模糊迴歸參數的估計方法,其結果對觀測樣本的解釋將更為合理,且具有模糊不偏的特性。在分析過程中,我們亦提出一些模糊統計量如模糊期望值、模糊變異數、模糊中位數的定義,以增加對這些參數的模糊理解。最後在本文中也針對台灣景氣指標與經濟成長率作實務分析,說明模糊迴歸模式的適用性。 / Conventional study on the regression analysis is based on the conception that the uncertainty of observed data comes from the random property. However, in this paper we consider both of the random property and the fuzzy perception to construct the regression model by using of fuzzy random variables. For the fuzzy sample (x<sub>i</sub>,Y<sub>i</sub>), we will process the parameters estimation of the fuzzy regression, and we call this process as fuzzy regression analysis. The parameters estimation for a fuzzy regression model is generally derived by the linear programming scheme. But it's result usually doesn't sufficiently reflect the characteristics of the observed samples. Hence in this paper we propose an alternative technique for parameters estimation in constructing the fuzzy regression model. The result will describe the observed data better than the conventional method did, moreover it will have the fuzzy unbiased properties. For the purpose of fuzzy perception on the fuzzy random variables, we also give definitions for certain important fuzzy statistics such as fuzzy expected value, fuzzy variance and fuzzy median. Finally, we give an example about the Taiwan Business Cycle and the Taiwan Economic Growth Rate for illustration.
22

Cox模式有時間相依共變數下預測問題之研究

陳志豪, Chen,Chih-Hao Unknown Date (has links)
共變數的值會隨著時間而改變時,我們稱之為時間相依之共變數。時間相依之共變數往往具有重複測量的特性,也是長期資料裡最常見到的一種共變數形態;在對時間相依之共變數進行重複測量時,可以考慮每次測量的間隔時間相同或是間隔時間不同兩種情形。在間隔時間相同的情形下,我們可以忽略間隔時間所產生的效應,利用分組的Cox模式或是合併的羅吉斯迴歸模式來分析,而合併的羅吉斯迴歸是一種把資料視為“對象 時間單位”形態的分析方法;此外,分組的Cox模式和合併的羅吉斯迴歸模式也都可以用來預測存活機率。在某些條件滿足下,D’Agostino等六人在1990年已經證明出這兩個模式所得到的結果會很接近。 當間隔時間為不同時,我們可以用計數過程下的Cox模式來分析,在計數過程下的Cox模式中,資料是以“對象 區間”的形態來分析。2001年Bruijne等人則是建議把間隔時間也視為一個時間相依之共變數,並將其以B-spline函數加至模式中分析;在我們論文的實證分析裡也顯示間隔時間在延伸的Cox模式中的確是個很顯著的時間相依之共變數。延伸的Cox模式為間隔時間不同下的時間相依之共變數提供了另一個分析方法。至於在時間相依之共變數的預測方面,我們是以指數趨勢平滑法來預測其未來時間點的數值;利用預測出來的時間相依之共變數值再搭配延伸的Cox模式即可預測未來的存活機率。 / It is so called “time-dependent covariates” that the values of covariates change over time. Time-dependent covariates are measured repeatedly and often appear in the longitudinal data. Time-dependent covariates can be regularly or irregularly measured. In the regular case, we can ignore the TEL(time elapsed since last observation) effect and the grouped Cox model or the pooled logistic regression model is employed to anlalyze. The pooled logistic regression is an analytic method using the“person-period”approach. The grouped Cox model and the pooled logistic regression model also can be used to predict survival probablity. D’Agostino et al. (1990) had proved that pooled logistic regression model is asymptotically equivalent to the grouped Cox model. If time-dependent covariates are observed irregularly, Cox model under counting process may be taken into account. Before making the prediction we must turn the original data into“person-interval”form, and this data form is also suitable for the prediction of grouped Cox model in regular measurements. de Bruijne et al.(2001) first considered TEL as a time-dependent covariate and used B-spline function to model it in their proposed extended Cox model. We also show that TEL is a very significant time-dependent covariate in our paper. The extended Cox model provided an alternative for the irregularly measured time-dependent covariates. On the other hand, we use exponential smoothing with trend to predict the future value of time-dependent covariates. Using the predicted values with the extended Cox model then we can predict survival probablity.

Page generated in 0.0141 seconds