前言：全球平均餘命普遍提升之情況下，認知障礙年數亦會跟著延長。透過健康餘命，結合年齡特定的發生率和死亡率，估計個體生活在不同健康狀態的平均時間。過去相關研究普遍認為低教育程度者更可能遭遇認知障礙，且高教育程度者平均餘命、認知健康餘命皆大於低教育程度者，即活得較久、較健康，而高教育程度者一旦發生障礙後存活年數極短，有快速衰退之現象，過去研究者根據認知儲備理論解釋。本研究將以方法學的角度進行剖析，期望透過臺灣調查資料之實證數據，與國際進行對話，提供政府部門未來長期照護相關政策規劃之參考。

材料方法：本研究採用TLSA長期追蹤調查，納入1999、2003、2007年三波調查，並串聯衛生福利部死因統計檔。納入分析對象為至少有2波調查資料，或僅有1波調查資料但有死亡資料者，且其他共變項資料沒有缺漏。使用多重狀態轉移模型進行分析，利用多元邏輯斯迴歸，加入教育程度、年齡與可隨時間變動之共變項，以本研究之65歲以上中高齡者長期追蹤資料，估計各年齡層的狀態間轉移機率（認知障礙發生機率、認知障礙後死亡機率），建構多重狀態生命表後，估算不同教育程度者的65歲平均餘命、認知健康餘命、認知障礙年數。又為了解罹患認知障礙後的死亡風險，以Cox比例風險模式估算認知狀態轉換之風險值。

結果與討論：本研究結果發現，低教育程度者65歲平均餘命為18.86年，認知健康餘命為15.50年，認知障礙年數為3.36年。與低教育程度者相比後發現，高教育程度者比低教育程度者多存活了2.02年，認知健康餘命多了4.61年，認知障礙年數少了2.59年。而男、女性有相同的趨勢，且女性教育程度間之差距更加明顯。結果皆顯示，無論男、女性都呈現高教育程度者之平均餘命較長，認知健康餘命較長，其不健康年數極短，一但罹患認知障礙很快過渡到死亡。但透過認知障礙年數計算之剖析，從男、女性65歲至100歲認知障礙發生機率，低教育程度者皆大於高教育程度者，可發現高教育程度者其累積障礙人年數經整體平均後必然較短，應以認知障礙者人數進行平均，方可比較教育程度差異之認知障礙後存活狀況。且男、女性65歲至100歲認知障礙後死亡機率，低教育程度者皆大於高教育程度者，亦違背高教育程度者認知障礙後較快速過渡死亡一說。進一步釐清教育程度對認知障礙後死亡的效應，控制基本人口學、健康行為與疾病狀態後，以低教育程度者為參考組，高教育程度者呈現0.85倍（95% C.I.= 0.82–0.88）之死亡風險。再加以控制認知障礙發病年齡，發現高教育程度者之死亡效應降低為0.67倍（95% C.I.= 0.64–0.69），可見認知障礙發病年齡為一種重要之干擾因子。

結論：本研究針對高教育程度認知障礙年數較短提供方法學上的見解，受到高教育程度認知障礙發生機率較低所影響，導致累積障礙人年較短，而非能代表高教育程度者認知障礙後之存活情形較差。而本篇研究為臺灣第一篇以認知障礙為失能指標，呈現65歲以上高齡者平均餘命、認知健康餘命，並可拆解各種共變項之組合下之更精確的餘命結果，未來可提供實證數據作為政策擬定與醫療、長照資源分配之參考。

SUMMARY
The aim of this article is to investigate the potential impact of education on life years with cognitive impairment from the perspective of methodology. The study sample is population based longitudinal data on people aged 65 years and older from Taiwan Longitudinal Study on Aging (TLSA) between 1999 and 2007. The included subjects were at least two waves of survey data, or only one wave of survey data but death data, and there were no missing data on other variables. Then we conducted multistate models to estimate life years with cognitive impairment, and Cox proportional hazard model for the risk of states transition. The result showed that both male and female with high education have longer life expectancy, life years without cognitive impairment, but very short years with cognitive impairment that once suffering from cognitive impairment, people with high education rapidly declines to death. However, the probability of cognitive impairment between men and women aged 65 to 100 with low education are greater than high education, it leads to be shorter years life with cognitive impairment for people with high education. To further clarify the effect of education on death after cognitive impairment, we not only found the more protective effect, but also that the age at onset of cognitive impairment is an important confounder.

INTRODUCTION
The length of life years with cognitive impairment will increase as total life expectancy increases. Healthy life expectancy, the average years who lives without cognitive impairment, combined age-specific morbidity and mortality to be used by policy makers and researchers to monitor the overall health of a population. In Previous studies based on cognitive reserve theory have shown that people with low education have higher risk of cognitive impairment, while those with higher education live longer and healthier. However, clinical disease onset triggers fast decline in cognition and increased mortality among those with high education. The aim of this article is to investigate the potential impact of education on life years with cognitive impairment from the perspective of methodology, and provide for policy-making, planning, and allocation of health and welfare resources.

MATERIALS AND METHODS
We used three waves of the Taiwan Longitudinal Study on Aging (TLSA) between 1999 and 2007, collected population based longitudinal data on people aged 65 years and older including measures of education and cognitive impairment, using the Short Portable Mental Status Questionnaire (SPMSQ). The included subjects were at least two waves of survey data, or only one wave of survey data but death data, and there were no missing data on other variables.
Life years with cognitive impairment was calculated using multistate models, allowing transitions between health and cognitively impaired states and from each of these states to death and allowing transition rates to vary across age, education, and other variables. To clarify the risk of death after cognitive impairment, the Cox proportional hazard model was used to estimate the risk of states transition.

RESULTS AND DISCUSSION
Analyses showed that people with low education can expect to live 18.86 years, 15.50 years without cognitive impairment, and 3.36 years with cognitive impairment. Compared with those with low education, people with high education can live more than 2.02 years , 4.61 years without cognitive impairment, but less than 2.59 years with cognitive impairment. Both male and female with high education have longer life expectancy, life years without cognitive impairment, but very short years with cognitive impairment that once suffering from cognitive impairment, people with high education rapidly declines to death. However, the probability of cognitive impairment between men and women aged 65 to 100 with low education are greater than high education, it leads to be shorter cumulative cognitive impairment person year for people with high education, and can’t compare to the survival of education group after cognitive impairment. Also men and women aged 65 to 100 years old with low education have a higher probability of death after cognitive impairment than high education, it is inconsistent with the rapid decline after cognitive impairment in high education.
To further clarify the effect of education on death after cognitive impairment, controlling for sex, age, healthy behavior and disease status, analyses showed 0.85 (95% CI= 0.82–0.88) for people with high education. Then, the age of onset was controlled, the death effect of those with high education was decreased to be 0.67 (95% C.I.= 0.64–0.69). This indicates that the age at onset is an important confounder.
CONCLUSSION
This study provides methodological insights that the shorter life years with cognitive impairment in high education are affected by the low incidence of cognitive impairment, and not represented people with high education have poor survival after cognitive impairment.
This is the first study in Taiwan to estimate the life expectancy, life years without cognitive impairment over aged 65 with the combination of covariates. The empirical data can be provided for future policy formulation and medical and long-term resource allocation.

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