Trong kinh te hoc, đinh luat Okun (đat theo ten cua Arthur Melvin Okun, nguoi đe xuat đinh luat nay vao nam 1962 )  cho biet moi quan he giua that nghiep va muc sut giam san luong cua 1 quoc gia, đuoc đuc ket tu quan sat thuc nghiem.  "Phien ban gap" cho biet voi moi 1% tang len cua  ti le that nghiep, GDP se giam tuong đuong 2% so voi GDP tiem nang.  "Phien ban sai phan" mo ta moi quan he giua muc thay đoi cua ty le that nghiep so voi GDP thuc tren co so du lieu quy. Tinh on đinh va huu dung cua đinh luat nay đen gio van con gay tranh cai.


Tinh khong hoan hao Đinh luat Okun, mot cach chinh xac, thuong đuoc xem la mot dang "Quy luat ngon tay cai" boi vi no la uoc luong xap xi đuoc rut ra tu quan sat thuc nghiem thay vi tu ly thuyet. Goi la xap xi vi con co nhung yeu to khac (nhu nang suat) anh huong đen ket qua. Trong ban bao cao goc cua Okun phat bieu rang 2% gia tang trong san luong se dan đen ty le that nghiep chu ky giam 1%, so nguoi tham gia luc luong lao đong tang 0.5%, so gio lam viec cua moi lao đong tang 0.5%; va san luong trong moi gio lam viec (nang suat lao đong) tang 1%.
Đinh luat Okun cho biet ty le that nghiep tang len moi 1 điem phan tram se dan đen tang truong GDP thuc giam 2%. Du vay, cac nha nghien cuu van đang tranh luan khi xem xet anh huong cua khung thoi gian va quoc gia đuoc chon len ket qua.
Moi quan he đuoc kiem đinh bang cach hoi quy toc đo tang truong GDP hoac GNP theo muc thay đoi cua ty le that nghiep. Martin Prachowny đa uoc luong đuoc rang san luong cu giam 3% lai dan đen ty le that nghiep tang 1%. Tuy nhien, tac gia cung tranh luan rang thuc te muc giam san luong phan lon do anh huong cua cac yeu to khac ben canh ty le that nghiep. Khi giu cho cac yeu to khac khong đoi, tac gia uoc luong muc giam san luong giam bot khoang 0.7% (Prachowny 1993). Tai My, muc sut giam san luong duong nhu co xu huong giam bot theo thoi gian. Theo Andrew Abel va Ben Bernanke, voi khung thoi gian nghien cuu gan hon đa uoc luong san luong giam khoang 2% tuong ung voi moi 1% tang cua that nghiep (Abel & Bernanke, 2005).
Co mot so nguyen nhan giai thich tai sao GDP co the tang/giam nhanh hon tuong ung muc giam/ tang cua ty le that nghiep:
Khi that nghiep tang,

Hieu ung so nhan tien te giam do nguoi lao đong co xu huong giam bot chi tieu 
Mot luong nguoi that nghiep tu bo tim kiem viec lam, va khong đuoc tinh vao luc luong lao đong. Khong đuoc thong ke la that nghiep. 
Cong nhan co the lam viec it gio hon
Nang suat lao đong co the giam, co le boi vi chu lao đong duy tri so cong nhan nhieu hon muc can thiet
Mot ham y tu cac phan tich tren đo la su gia tang nang suat lao đong hoac su mo rong quy mo luc luong lao đong co the dan đen tang truong san luong rong nhung ty le that nghiep rong khong giam (hien tuong "jobless growth"). 


Trinh bay Toan hoc Phien ban gap cua Okun (Abel & Bernanke 2005) co the viet nhu sau:

  
    
      
        (
        Y
        −
        
          
            Y
            ¯
          
        
        )
        
          /
        
        
          
            Y
            ¯
          
        
        =
        −
        c
        (
        u
        −
        
          
            u
            ¯
          
        
        )
      
    
    {\displaystyle (Y-{\overline {Y}})/{\overline {Y}}=-c(u-{\overline {u}})}
  
, voi

  
    
      
        Y
      
    
    {\displaystyle Y}
  
 la san luong thuc te

  
    
      
        
          
            Y
            ¯
          
        
      
    
    {\displaystyle {\overline {Y}}}
  
 la san luong tiem nang

  
    
      
        u
      
    
    {\displaystyle u}
  
 la ti le that nghiep thuc te 

  
    
      
        
          
            u
            ¯
          
        
      
    
    {\displaystyle {\overline {u}}}
  
 la ti le that nghiep tu nhien

  
    
      
        c
      
    
    {\displaystyle c}
  
 la he so phan anh moi quan he giua thay đoi cua ty le that nghiep va thay đoi cua san luong 
Tai My tu nam 1955 tro đi, gia tri cua c nhu đa trinh bay nam trong khoang tu 2 đen 3.
Phien ban gap, nhu đa trinh bay o tren, thi rat kho khi ung dung vi 
  
    
      
        
          
            Y
            ¯
          
        
      
    
    {\displaystyle {\overline {Y}}}
  
 va 
  
    
      
        
          
            u
            ¯
          
        
      
    
    {\displaystyle {\overline {u}}}
  
 chi co the uoc luong chu khong the thong ke hay đo luong. Mot dang pho bien hon cua Đinh luat Okun, su dung muc thay đoi cua san luong so voi muc thay đoi cua that nghiep, duoi dang nhu sau:

  
    
      
        Δ
        Y
        
          /
        
        Y
        =
        k
        −
        c
        Δ
        u
        
      
    
    {\displaystyle \Delta Y/Y=k-c\Delta u\,}
  
, voi:

  
    
      
        Y
      
    
    {\displaystyle Y}
  
 va 
  
    
      
        c
      
    
    {\displaystyle c}
  
 nhu đinh nghia o tren

  
    
      
        Δ
        Y
      
    
    {\displaystyle \Delta Y}
  
 la muc thay đoi cua san luong thuc te 

  
    
      
        Δ
        u
      
    
    {\displaystyle \Delta u}
  
 la muc thay đoi cua that nghiep thuc te

  
    
      
        k
      
    
    {\displaystyle k}
  
 la toc đo tang truong binh quan theo nam cua san luong toan dung
Hien tai o My, k la khoang 3% va c la khoang 2, vay cong thuc co the viet lai nhu sau:

  
    
      
        Δ
        Y
        
          /
        
        Y
        =
        0.03
        −
        2
        Δ
        u
        .
        
      
    
    {\displaystyle \Delta Y/Y=0.03-2\Delta u.\,}
  


Phep lay đao ham cho dang toc đo tang truong Chung ta  bat đau voi dang thu nhat cua Đinh luat Okun:

  
    
      
        (
        
          
            Y
            ¯
          
        
        −
        Y
        )
        
          /
        
        
          
            Y
            ¯
          
        
        =
        1
        −
        Y
        
          /
        
        
          
            Y
            ¯
          
        
        =
        c
        (
        u
        −
        
          
            u
            ¯
          
        
        )
      
    
    {\displaystyle ({\overline {Y}}-Y)/{\overline {Y}}=1-Y/{\overline {Y}}=c(u-{\overline {u}})}
  

  
    
      
        −
        1
        +
        Y
        
          /
        
        
          
            Y
            ¯
          
        
        =
        c
        (
        
          
            u
            ¯
          
        
        −
        u
        )
        .
      
    
    {\displaystyle -1+Y/{\overline {Y}}=c({\overline {u}}-u).}
  

Lay đao ham 2 ve,ta co

  
    
      
        Δ
        (
        Y
        
          /
        
        
          
            Y
            ¯
          
        
        )
        =
        (
        Y
        +
        Δ
        Y
        )
        
          /
        
        (
        
          
            Y
            ¯
          
        
        +
        Δ
        
          
            Y
            ¯
          
        
        )
        −
        Y
        
          /
        
        
          
            Y
            ¯
          
        
        =
        c
        (
        Δ
        
          
            u
            ¯
          
        
        −
        Δ
        u
        )
        .
      
    
    {\displaystyle \Delta (Y/{\overline {Y}})=(Y+\Delta Y)/({\overline {Y}}+\Delta {\overline {Y}})-Y/{\overline {Y}}=c(\Delta {\overline {u}}-\Delta u).}
  

Quy đong mau so, ta co:

  
    
      
        (
        
          
            Y
            ¯
          
        
        Δ
        Y
        −
        Y
        Δ
        
          
            Y
            ¯
          
        
        )
        
          /
        
        (
        
          
            Y
            ¯
          
        
        (
        
          
            Y
            ¯
          
        
        +
        Δ
        
          
            Y
            ¯
          
        
        )
        )
        =
        c
        (
        Δ
        
          
            u
            ¯
          
        
        −
        Δ
        u
        )
        .
      
    
    {\displaystyle ({\overline {Y}}\Delta Y-Y\Delta {\overline {Y}})/({\overline {Y}}({\overline {Y}}+\Delta {\overline {Y}}))=c(\Delta {\overline {u}}-\Delta u).}
  

Nhan ve trai voi 
  
    
      
        (
        
          
            Y
            ¯
          
        
        +
        Δ
        
          
            Y
            ¯
          
        
        )
        
          /
        
        Y
      
    
    {\displaystyle ({\overline {Y}}+\Delta {\overline {Y}})/Y}
  
 ,ta co

  
    
      
        (
        
          
            Y
            ¯
          
        
        Δ
        Y
        −
        Y
        Δ
        
          
            Y
            ¯
          
        
        )
        
          /
        
        (
        
          
            Y
            ¯
          
        
        Y
        )
        =
        Δ
        Y
        
          /
        
        Y
        −
        Δ
        
          
            Y
            ¯
          
        
        
          /
        
        
          
            Y
            ¯
          
        
        ≈
        c
        (
        Δ
        
          
            u
            ¯
          
        
        −
        Δ
        u
        )
      
    
    {\displaystyle ({\overline {Y}}\Delta Y-Y\Delta {\overline {Y}})/({\overline {Y}}Y)=\Delta Y/Y-\Delta {\overline {Y}}/{\overline {Y}}\approx c(\Delta {\overline {u}}-\Delta u)}
  

Ta gia đinh 
  
    
      
        Δ
        
          
            u
            ¯
          
        
      
    
    {\displaystyle \Delta {\overline {u}}}
  
, la muc thay đoi cua ty le that nghiep tu nhien bang 0. Ta cung gia đinh 
  
    
      
        Δ
        
          
            Y
            ¯
          
        
        
          /
        
        
          
            Y
            ¯
          
        
      
    
    {\displaystyle \Delta {\overline {Y}}/{\overline {Y}}}
  
, toc đo tang truong cua san luong toan dung, xap xi bang voi gia tri trung binh cua no, 
  
    
      
        k
      
    
    {\displaystyle k}
  
. Vi vay, ta co:
  
    
      
        Δ
        Y
        
          /
        
        Y
        ≈
        k
        −
        c
        Δ
        u
        .
      
    
    {\displaystyle \Delta Y/Y\approx k-c\Delta u.}
  


Su huu ich Thong qua so sanh giua du lieu thuc te va du bao ly thuyet, Đinh luat Okun la mot cong cu đang gia trong du bao xu huong giua ty le that nghiep va san luong GDP thuc. Tuy nhien, ve muc đo chinh xac cua du lieu, thong qua viec so sanh ket qua tu Đinh luat Okun voi so lieu thuc te, đa cho thay la thieu chinh xac. Đo la vi ton tai phuong sai trong uoc luong tham so. Cac ket luan rut ra tu Đinh luat Okun co the chap nhan đuoc o mot chung muc nhat đinh. Mat khac, mot vai phat hien cho thay la Đinh luat Okun co khuynh huong chinh xac hon voi cac du bao ngan han hon la dai han. Cac nha du bao đa xac nhan đieu nay la đung vi cac đieu kien thi truong khong luong truoc co the anh huong len cac tham so cua Okun.
Nhu vay, Đinh luat Okun noi chung la chap nhan đuoc voi cac nha du bao kinh te nhu la mot cong cu phan tich xu huong ngan han hon la cho cac phan tich dai han hay cac tinh toan đoi hoi su chinh xac.


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Abel, Andrew B. & Bernanke, Ben S. (2005). Macroeconomics (5th ed.). Pearson Addison Wesley. ISBN 0-321-16212-9.
Baily, Martin Neil & Okun, Arthur M. (1965) The Battle Against Unemployment and Inflation: Problems of the Modern Economy. New York: W.W. Norton & Co.; ISBN 0-393-95055-7 (1983; 3rd revised edition).
Case, Karl E. & Fair, Ray C. (1999). Principles of Economics (5th ed.). Prentice-Hall. ISBN 0-13-961905-4.
Okun, Arthur M. (1962). "Potential GNP, its measurement and significance". Cowles Foundation, Yale University.
Knotek, Edward S.  "How Useful Is Okun's Law." Luu tru ngay 17 thang 12 nam 2010 tai Wayback Machine Economic Review, Federal Reserve Bank of Kansas City, Fourth Quarter 2007, pp. 73–103.
Prachowny, Martin F. J. (1993). "Okun's Law: Theoretical Foundations and Revised Estimates,"  The Review of Economics and Statistics, 75 (2), pp. 331–336.
Gordon, Robert J., Productivity, Growth, Inflation and Unemployment, Cambridge University Press, 2004
McBride, Bill (ngay 11 thang 10 nam 2010). "Real GDP Growth and the Unemployment Rate". Calculated Risk. Truy cap ngay 5 thang 12 nam 2010.