Nguyen Tran Hien Ths.. Hoang Thi Hoa..[r]
(1)(2)(3)T R U O N G DAI HOC Y HA NOI ■ ■ ■ BO MON DICH T i HOC• • ■
T H I T C H A N H D I C H T i H O C
(T ban Ian thti h a i co siia chiia va bo sung)
m HOC THAI NGircM
(4)C h u b ie n :
PGS.TS Ducing Dinh Thien
T h a m g ia b ie n so a n : PGS.TS Le Vu Anh Ths Tran Van Chi
(5)LOI NOI DAU
De phuc vu nhu cau hoc tap cua sinh vien cac cap hoc cua TrUcfng Dai hoc Y Ha Noi, chung toi bien soan cuon "Thtfc hanh Dich t§ hoc" nham minh hoa cho phan ly thuyet v'e phudng phap Dich t l hoc hien dai va nang cao k h i nang thifc hanh thiJc te cua anh chi em No cung co' the giup ich it nhieu cho can bo lam cong tac dich t! va cac can bo nghien cdu y hoc v'e phtfdng phap hoc chuan mtfc
Cuon sach chac chan chtfa dung nhung thieu sot n hat dinh Cac tac gi& chan cAm on va tiep thu nhung chi giao cua dong nghiep xa gan
Ha noi, thang nam 1995 Thay m at Tap the tac gia
(6)PGS.TS DiiOng Dinh Thien
T h a m g ia b ie n so a n : PGS.TS Le Vu Anh Ths Tran Van Chi
(7)l o i n o i d a u
De phuc vu nhu cau hoc tap cua sinh vien cac cap hoc cua Trudng Dai hoc Y Ha Noi, chung toi bien soan cuon "ThiJc hanh Dich t i hoc" nham minh hoa cho phan ly thuyet v'e phuong phap Dich t l hoc hien dai va nang cao khd nang thuc hanh thiic te cua anh chi em No cung co the giup ich it nhieu cho can bo lam cong tac dich t l va cac can bo nghien cdu y hoc v'e phuong phap hoc chuan mile
Cuon sach chac chan chtfa dung nhung thieu sot nhat djnh Cac tac gi& chan c^m on va tiep thu nhiitng chi giao cua dong nghiep xa gan
Ha noi, thang nam 1995 Thay m at Tap the tac gia
(8)(9)TY LE MAC
I MUC TIEU
1 Dinh nghia va phan biet duoc ty le mdi mac va ty le hien mac Neu moi tuong quan va ling dung cua hai loai ty le mac tren day
3 Liet ke nhilng yeu to co the gay nen sil khac qua trinh tinh toan ty le mdi mac va ty le hien mac
II NOI DUNG
Mot nhung muc tieu co b&n cua dich t l hoc nham nghien cdu ve svJ xuat hien benh hay mot tran g thai sinh ly hoac mot hien tifpng siic khoe nao xa hoi Viec ludng sil xuat hien benh ta t la nhiem vu trung tam, song cua dich te hoc
Co the lucmg sU xuat hien benh theo nhi'eu cach khac nhau:
1 So tu y et doi va so tu o n g doi lien quan tdi kich thildc quan the.
Dich t l hoc khac v6i nhting mon y hoc lam sang d hai diem quan trong: Thtf nhat, cac nha dich t l hoc quan tam nghien ctfu m6t nhom ngtfcri chii khong ph4i tifng ca the rieng biet Thii hai, cac nha dich t l hoc nghien criu c& nhiitng ngUcfi dupe coi la khoe manh lSn nhfing ngii5i om dau, ho co gang tim kiem sU khac biet ca b&n giiia nhung ngUdi Cac nha dich t l hoc co gang ludng sii xuat hien benh ta t nhung quan the khac De co the so sanh sU xuat hien benh d cac quan the co ldch thtfdc khac thi dieu can thiet la tinh toan ty le Mot ty le bao gom hai phan sau:
Tut so So sif kien xky
M lu so Dan so co nguy co
(10)2 Ty le mdi m & c va ty le hien m&c.
Ty le mdi mac va ty le hien mac la hai hinh thai ludng chu yeu v'e sU xuat hien benh dich t l hoc.
a) ty le hien mtic.
Ty le hien mac thudng dUdc ky hieu la P NgUdi ta goi ty le bang mot thuat ngU khac la ty so hien mac Ty le hien mac dUdc dinh nghla nhu sau:
Tong so cac trUdng hdp benh/thdi diem/quan the p = -Tong dan so cua quan the thdi diem
Ty le hien mac ludng so ngUdi mac benh mot quan the tai thdi diem nhat dinh Tuy nhien ty le hien mac phu thuoc vao hai yeu to la ty le mdi mac va thai gian keo dai trung binh cua benh day neu ty le hien mac mot benh bat ky nao co su thay doi thi ty le da phan anh sU thay doi cua ty le mdi mac hoac thdi gian keo dai trung binh cua benh hoac ca hai Ty le hien mac giong nhu ty so dan so mac benh mot quan the nhat dinh tai mot thdi diem Nhu vay ty le co gia tri di tU den
b) ty le mdi mac tich luy.
Ty le mdi mac tich luy co ten goi la ty so m6i mac, ky hieu la Cl Ty le mdi mac tich luy dUdc dinh nghia nhu sau:
So ca the mdi mac benh thdi gian nghien cUu CI=
-Tong so dan cua quan the nghien cUu tai thdi diem bat dau nghien cUu
Nhu vay, ty le mdi mac rich luy chinh la ty so cua cac ca the khong co benh tai thdi diem ban dau nghien cUu, nhung da phat trien benh giai doan nghien cUu Ty le lildng nhCfng trUdng hdp benh mdi xuat hien mot quan the mot thdi gian nhat dinh Hay noi cach khac, ty le mdi mac tich luy dUdc xem nhii nguy cd trung binh cua ca the quan the cd the mac benh mot thdi gian nhat dinh O day, cong thiic tinh ty le cho thay tti so la mot phan cua m iu so, ty le cd gia tri di tti den
Trong mdt so nghien culu nhilng nhom dan ctf khac quan the nghien criu da dan den sU khac biet ve nguy cd mac benh Su khac biet cua nhung nhom dan cu quan the nghien criu d day chu yeu la thdi gian theo doi dUdc doi vdi tting ca the Xuat phat ti* thuc te rang nghien criu tildng lai nhting ca the tham gia nghien criu khac theo thdi gian, cd nhung ca the tham gia tif luc bat dau cho den ket thuc Nhung co kha nhieu ca the ru t khoi nghien ciiu theo cac thdi diem khac cd the vi khong muon tham gia nghien ctfu, hoac da di ctf thdi gian nghien ciiu Trong tinh tran g thi ty le mdi mac tich luy khong the tinh dUdc tnJc tiep til nhilng so lieu nhu vay (d day, dai thdi gian quan sat doi vdi tifng ca the anh hudng true tiep den ty le mdi mac rich luy) ma phai dung tdi khai niem m at mdi mac sau day
c) M dt mdi mac (Ky hieu la ID).
(11)nhu sau:
Tong so trUdng hop benh mdi mac x&y quan the mot kho&ng thdi gian nhat dinh
ID = - -Tong so dcfn vi dai thdi gian cd nguy cd theo doi
dUdc doi vdi tifng ca the quan the
M iu so la tong so dai thdi gian co' nguy cd mac benh Ddn vi thudng dUdc ludng theo nam va bieu thj la "Nam-NgUdi" hay "Thdi gian-NgUdi" hoac "Thdi gian cd nguy cd" Doi vdi tim g ca the quan the nghien cUu, thdi gian co' nguy cd la thdi gian ma do' tUng ca the tham gia nghien cUu quan the giu dUdc tinh trang khong mac benh
Bang cach chia so trUdng hdp benh mdi mac cho thdi gian co' nguy cd thi dai thdi gian cua ttfng ca the tham gia nghien cUu cung nhu tong so dai thdi gian quan sat da dUdc tinh den
Ty le mdi mac ludng ty le phat trien benh mot thdi gian nhat dinh Ty le mdi mac phan anh toe xuat hien benh Mot sU thay doi ve ty le mdi mac thi co' nghia la da co' sU thay doi ve can bang cua cac yeu to can nguyen Ty le mdi mac la mot ty le cd ban t quan doi vdi cac nha nghien cUu tim can nguyen gay benh
Tren thuc te, ngUdi ta khong the tinh thdi gian cd nguy cd cho tilng ca the, ma la Udc tinh thdi gian co' nguy cd tUdng doi Chung ta co' the tinh bang cach cong dan so dau luc bat dau thdi gian nghien cUu va dan so cuoi thdi gian nghien cUu, sau do' chia cho va nhan vdi dai thdi gian nghien cUu Nhu vay kich thudc dan so d thdi diem giUa cua thdi gian nghien cUu co' the dUdc sti dung theo cach tinh tUdng doi nhu tren
Mat mdi mac khong phai la ty so nhu ty le tren vi tut so la so trUdng hop mdi mac benh, m iu so la so ddn vi thdi gian-ngudi Tri so cua m at mdi mac khong bao gid nho hdn
3 Moi qu an h e giufa cac ty le tren.
Ty le hien mac phu thuoc vao ty le mdi mac va thdi gian keo dai trung binh cua benh Ty le hien mac la san pha’m cua ty le mdi mac va thdi gian keo dai cua benh Trong nhUng
tinh tran g o’n dinh nhu cac benh man tinh chang han, thi moi quan he giUa ty le mdi mac va ty le hien mac co' the dUdc bieu thi nhu sau:
P = I x D Trong P = Ty le hien mac
I = Ty le mdi mac
D = Thdi gian keo dai trung binh cua benh
Moi lien quan giUa cac ty le cd the thay ro hinh ve sau day:
Cac nha lap ke hoach cho nhUng hoat dong y te thudng dua tren ty le hien mac vi ty le ludng nhu cau nhu nhu cau giudng benh cung nhu nhung tran g thiet bi y te va nhu cau ve nhan luc
(12)If)n h - Moi lien q u an giUa s6 tn ld n g hdp mdi m ac va hien mac
dinh cac nghien cUu theo doi ve tuang lai bang cach theo doi mot quan the nhat dinh ma khdi diem nghien cUu tilng ca the tham gia da dUOc xac dinh khong mac benh ma ta dinh nghien cviu, sau ngudi ta tien hanh theo doi tilng ca the mot thai gian nhat dinh de xac dinh nhung trUdng hop benh mdi xuat hien va danh gia toe phat trien benh Ty le mdi mac duoc so sanh giUa cac nhom quan the cd phai nhiem vdi yeu to nguy ca d cac mUc khac nham ludng anh hudng cua cac yeu to nguy ca tdi su xuat hien benh Bang cach nay, ngudi ta cd the udc tinh nguy ca tuang doi (xem them chuang Nghien cUu tuang lai)
III BAI TAP
1 Moi mot duang k^ dam ngang dudi day bieu thj cho mot trUdng hap bi benh tang bach cau dan nhan nhilm khuan Dudng noi giUa hai diem bieu thi thdi ky bi benh cua tUng trUdng hap mang cac ky hieu khac (Gid sii rang quan the nghien cUu co dinh la 20 ngudi) Dua vao hinh ve sau day hay tinh cac ty le sau:
a) Tinh ty le mdi mac nam 1988 b) Tinh ty le hien mac trongnam 1988
c) Gia sijf co' mot cuoc di'eu tra tien hanh vao thang 7/1988 Hay tinh ty le hien mdc benh tai thdi diem
2 Tti so lieu d bang dudi day, hay tinh thdi gian keo dai trung binh cua tilng benh man tinh nhieu nam lien
(13)193 0 -1 8 0 - '2 -1 8 Bring 1- T Y L f H lf.N m A c V A T Y LI? M O I m A ( ' C U A B $ N H M A N
T IN H T A I M T O u A n T H fi X T IN H T R £ N 100.000 D A N
B enh le mSc tinh Iren 0 0 dan
Tv le hien miic _ _
Ty le mdi mSc
D ong kinli 376 30,8
Viem da khrtp 55 5,0
P arkinson 157 0
Henh ve day T K van d o n g 1.7
Benh khoi u T K T lf 69 17.3
3 Nghien cUu moi tuang quan giUa che an va benh tat, vi du ngudi ta bieu thi tinh hinh mac benh bang so tuyet doi (nhu tong so trUdng hap mac benh) hoac bieu thi bang s6 tu ang doi (con so cd lien quan tdi ldn cua quan the nghien cUu) Cach bieu thi nao la thich hap, hay giai thich
(14)5 Gia s\i mot quan the cd phan bo tuo’i on dinh, co' the co' cach ly giai nhu the nao ty le hien mAc cua benh gia tang, mac du ty le mdi mac vlln giu mUc hang dinh
6 Trong thdi gian nam tai mot phong thi nghiem y hoc ldn da cd 532 ngudi bi tai nan lao dong Con so ngudi lam viec tai day luc ban dau cua thdi ky la 520 ngudi va tinh den thdi diem cuoi cung la 680 ngudi NgUdi ta co' the tinh dupe ty le nao nghien cUu nay, hay tinh cu the
7 De co' the phat hien va dieu tri sdm ung thu cd tCr cung, ngudi ta tien hanh kham s&n khoa hang loat va thudng xuyen cho phu nU tuoi til 30 den 59 Sau do' tiep tuc theo doi va phat hien nhUng phu nU mdi bi benh mot kho&ng thdi gian nghien cUu nhat dinh Neu tinh til thdi diem bat dau cho den ket thuc ngudi ta tinh duoc khoing thdi gian nguy cd la 338294 nam-ngUdi va xac dinh dupe 123 ca benh mdi xuat hien suot thdi gian nghien cUu Co' the tinh dupe ty le nao nghien cUu nay, hay tinh cu the
8 Trong mot nghien cUu sang loc tien hanh tren 5000 phu nU Ngudi ta da tim thay co' 25 ngudi mac benh ung thu vu Nam nam sau do', ngudi ta da phat hien them 10 trUdng hop bi benh Cd the tinh dupe nhUng ty le nao nghien cUu nay, hay tinh cu the?
9 Cd 270 trUdng hop bi benh loet ta tran g d nam gidi thdi gian nam nghien cUu theo doi tai mot Tong so nhung ngudi dan ong sinh song la 18500 ngudi, thdi diem luc bat dau nghien cUu va 21500 ngudi vao thdi diem cuoi cua cuoc dieu tra Ngudi ta co' the tinh dupe ty le nao, hay tinh cu the?
10 Theo trung tam nghien cUu ung thu cua Thuy Dien, tinh til nam 1971, 1972 va 1973 cd so trUdng hop bi ung thu lan lupt tilng nam la 97, 121 va 112 trUdng hpp nam gidi bi benh tuoi til 70-74 Tai thdi diem dau nam 1971 cd 309949 ngudi dan ong nhom tuoi va den cuoi nam 1973 cd 332400 dan ong cung nhom tuoi Ngudi ta co' the tinh dupe nhUng ty le nao dua tren cac du kien tren Hay tinh cu the
11 Trong mot nghien cUu sang loc tren 1329 nam gidi tuoi til 40 den 59 tuoi, ngudi ta da tien hanh kham kiem tra mUc cholesterol huyet va huyet ap tam trUdng cho nhung doi tUdng Sau tien hanh theo doi nhung doi tUdng tren vong nam nham phat hien nhung trUdng hpp bi benh nhoi mau cd tim Biet rang tai thdi diem bat dau nghien cUu ta t ca cac doi tUdng deu khong bi benh Ket qua nghien cUu dupe trinh bay bang dudi day
Bdng 2- M U C D () H U Y G t A P T A M T R U O N G (m m H g )
Mile c h o lestero l huyet th an h (mg/lOOml)
< 147-166 >
T o n g so T htip benh
'
T o n g s6 T.hrtp benh
T o n g so
T h d p benh
< 2 431 10 93 49
220-259 347 19 74 <> 49
> 185 19 57 11 44 11
(15)Dua vao being so lieu tren ngudi ta cd the tinh dupe loai ty le nao, hay tinh cac ty le doi vdi tilng trUdng hdp cu the sau:
a) Nhom dan ong co' luong cholesterol huyet dudi 220 mg/100ml va huyet ap tam trUdng dudi 147 mmHg
b) Nho'm dan ong co' ludng cholesterol huyet tUdng > 260 mg/100ml va huyet ap tam trUdng dudi 147mmHg
c) Nho'm dan ong co' mUc cholesterol huyet tUdng < 220 mg/100ml va huyet ap tam trUdng > 167mmHg
d) Nho'm dan ong co' mUc cholesterol huyet tUdng > 260 mg/lOOml va huyet ap tam trUdng > 167mmHg
TRA LOI BAI TAP a) 10/20 Hay 55%
b) 11/20 = 50% (10 trUdng hdp mdi mac + trUdng hdp mac til trUdc). c) 5/20 - 25%
2 Thdi gian keo dai trung binh cua benh ky hieu la D
D = Benh dong kinh =12,2
D = Viem da khdp =1,1
D = Parkinson =7,8
D = Benh ve day than kinh van dong =4,1
D = Benh khoi u he thong than kinh trung Udng =4,0
3 Con so tUdng doi Khi so sanh tinh trang benh tat, ngudi ta can ph&i ludng lam cho cac chi so bieu thi tinh trang benh doc lap vdi ldn cua quan the
4 a) 2% dan so bi benh tai mot thdi gian cu the nao
b) 5 trUdng hpp bi benh x&y tren 10000 nam-ngUdi co' nguy cd mac benh.
5 thdi gian keo dai trung binh cua benh gi&m So trUdng hdp mac benh = 532
520+680
Dan so tru n g binh = - - = 600 Thdi gian quan sat la nam
Tdng so thdi gian nguy cd la = 600 x 4 = 2400 nam-ngUdi 532
Ty le mdi mac (ID) = 24QQ = nam
7 Ty le mdi mac benh (ID) 123
(16)P = - = 0,005 5000
Ty le mdi mac tich luy Cl
10
Cl = - -— = 0,002 nam nghien cUu 1000 - 25
9 So trUdng hap mac benh la 270 18500 + 21500
Dan so trung binh = - = 20000 2
Thdi gian quan sat la nam
Tong so thai gian nguy ca = 20000 x = 100000 nam-ngUdi 270
Ty le mdi mac I = - = 0,0027 nam
100.000
25
TY LE T il VONG
I MUC TIEU
1 Viet dUdc dinh nghia cua cac ty le sau : a) Ty le tit vong tho
b) Ty le tii vong rieng phan (theo tuoi, giai, dan toe va theo nguyen nhan) c) Ty le chet/m ic (Case - Fatality Rates)
2 Phan tich, sii dung dung duac cac ty le tren Neu nhUng ly can phai chuan hoa ty le
II NOI DUNG
1 Ty le tii von g tho (CDR)
Tong so trUdng hdp chet vi moi nguyen nhan/qu'an the/thdi gian CDR =
-Dan so trung binh,'quan the/thdi gian
Neu tinh ty le tii vong tho vong nam thi tif so bao gom tong so tu vong nam, mau so chinh la dan so giua nam (30-6 hang nam)
(17)Ty le tijf vong tho rat de tmh, no' bieu thi ty le tii vong quan sat duac quan the nghien cUu va no la diem tinh toan khdi dau cho viec tinh toan cac ty le chuan hoa
Ty le tut vong tho ludng ty so tii vong cua mot quan the hang nam Ty le tii vong bi anh hudng bdi yeu to sau :
- ThU nhat la xac suat chet (yeu to duac ludng mot cach chinh xac bang ty le chet rieng phan theo tuoi, se giai thich d phan sau)
- Thu; hai la dac tru n g theo tuoi hay phan bo theo tuoi cua quan the dang xem xet ty le tuf vong tho
Do anh hudng cua yeu to tren, ngudi ta thudng xem xet ty le til vong rieng phan theo tuoi va cau true dan so cua quan the trudc tien hanh so sanh ty le til vong tho giUa cac nho'm quan the vdi
2 Tii vo n g va tuoi.
Tuoi la m ot nhung dac trUng quan nhat anh hudng tdi phan bo benh. Trudc khi cd the tien hanh so sanh phan bo tinh hinh benh tat giUa 2 quan the, ngudi ta can ph&i tinh den sU khac biet ve cau true tuoi giua 2 quan the nay.
Vi du: Tai Maine nam 1973 ty le til vong tho la 10,6 tren 1000 dan va tai Alaska cung nam ty le la 4,6 tren 1000 dan Dua tren ty le tii vong tho d 2 khu vUc tren cho thay ty le tOf vong d Maine cao hdn han Alaska, nhung xem xet sU phan bo tuoi tai quan the tren cho thay ty le tii vong tho d Maine cao quan the d day co' cau true dan so gia va tai Alaska co' cau true dan so tre mot each dien hinh
3 Ty le tii v o n g rien g phan (hoac ty le tii vo n g dac hieu) th eo tuoi.
Yeu to tuoi anh hudng sau sac len ty le tii vong tho vay dieu can thiet la tinh ty le tii vong tifng nho'm tuoi de so sanh Bang sau day trinh bay ty le tii vong tho la ty le tii vong rieng phan theo tuoi tai Baltimore cho thay : NgUdi da tran g tai Baltimore co' ty le tii vong tho cao han (15,2) ngudi da mau (9,8) N neu xem xet ty le tii vong tifng nho'm tuoi a ca nho'm ngudi lai cho thay hinh anh ngUdc lai la ngudi da mau cd ty le tii vong rieng phan tUng nho'm tuoi deu cao han ngudi da trang Vay dudng nhu co' sU mau th u in gi d day giua ty le tii vong tho va ty le tii vong rieng phan theo tuoi? Cau tra ldi d day la sU phan bo tuoi khac tai Baltimore khac biet giua ngudi da trang va ngudi da mau Nhung ngudi da tran g da phan la nhieu tuoi va nhUng ngudi da mau chu yeu la d lUa tuoi tre
Bang 1 - T Y LG T l’/ V O N G T IN H IKL-.N 0 D A N T U B ) T H O I V A C H U N G T O C T A I T H A N H PH (‘) B A L T IM O R E
T a t ca cac n h o m tuoi
I tuoi 1-4 5-17 18-44 45-65 >
D a Iran g 15.2 13.5 ,6 0,4 1,5 10.7 19.7
D a d e n 9.S 2 ,6 1.0 0,5 3.6 IS, 61.1
4 Ty le tii vo n g chuan hoa th eo tuoi.
(18)can phai tinh ty le tii vong chuan hoa theo tuoi
De co th e hieu ty le tii vong c h u a n hoa theo tuoi la gi va cach tfn h n h u th e nao? TrUdc h e t can phai b iet n g m ot ty le tu vong th o ch in h la to n g so cua cac phiic hdp
s a u d a y :
Ty so dan nho'm tuoi x ty le tii vong rieng phan cua nhom tuoi
Ty le tii vong tho dUdc chuan hoa bang cach diia sU khac biet ve dan so tung nhom tuoi tUdng ling vdi ty le dan so cac nho'm tuoi quan the chuan Quan the chuan thudng la quan the dUdc dieu tra cac cuoc dieu tra dan so
Trinh tu cach chuan hoa se dUdc minh hoa d vi du sau day:
/M ig 2-TY LP T l’f VONG O CONG DONG
C ong d o n g Ty le lil vong rieng phftn ih eo tufli/ 0
T re ' Gia
A 16
1?
Cong dong A co' dan so gom mot nOta ngudi tre va mot niia ngudi gia Cong dong B cd 2/3 ngudi tre va 1/3 ngudi gia song cong dong Ty le tii vong rieng phan tung cong dong d U d c dua d b&ng
TU cac thong tin tren, chung ta cd the tinh ty le tii vong tho cho cong dong nhu sau:
- Ty le tii vong tho d cong dong A la:
(1/2X4) + (1/2X16) = 10 tren 1000 - Ty le tu vong tho d cong dong B la:
(2/3X5) + (l/2)(20) = 10 tren 1000
Luu y rang mac dau xac suat chet d cong dong A la thap hdn d cac nho'm tuoi, nhung ty le tii vong tho lai tUdng tu nhu cong dong B vi rin g cong dong A cd dan so gia hdn cong dong B
Bay gid chung ta hay tinh ty le chet chuain hoa cho tung cong dong sii dung quan the chuan Quan the chuan duoc chon d day bao gom 1/3 la ngudi tr£ va 2/3 ngudi gia
- Ty le tii vong chuan hoa d cong dong A la: (1/3X4) + (2/3X16) = 12 tren 1000 - Ty le tii vong chuan hoa d cong dong B la: (l/3)(5) + (2/3X20) = 15 tren 1000
Ty le tii vong chuan hoa theo tuoi phan anh xac suat chet tUng cong dong va day chung ta co' the sii dung ty le so sanh ma khong so in h hudng su khac biet
(19)vie phan bo tuoi giua cong dong
5 Ty le tii v o n g dac hieu th eo gidi.
Noi chung da so cac nude tren the gidi ty le td vong d nam gidi thudng cao hon so vdi nd gidi Vi du d My nam 1973 ty le chet chuan hoa theo tuoi la 9,1 tren 1000 nam gidi, ty le d nd gidi chi chiem khodng mot nda: 5,1 Da cd kha nhieu cach gidi thich khac cho tinh trang nhu nam gidi thudng mac cac benh ma cd nguy co td vong cao nhu benh tim mach, ung thu, tai nan hoac cac benh ve dudng ho hap
6 Ty le ch et dac hieu th eo chu n g toe.
Vi du vUa neu tren da die cap cho thay ngudi da mau cd ty le td vong cao hon so vdi ngudi da trang Viec xem xet ty le td vong dac hieu theo cac chung toe khac va nguyen nhan td vong la rat can thiet
7 Ty le tii vo n g x e t th eo nguyen nhan
Ty le td vong mot nguyen nhan hay mot tinh trang benh ly nao cung cd the tinh cho toan bo quan the hoac cho bat cd mot nhom tuoi hay chung toe nao hoac cac nho'm tuoi xet theo sU khac biet ve gidi
Ty le td vong theo nguyen nhan dupe tinh nhu sau:
Tong so chet mot benh quan the nhat dinh mot khodng thdi gian nao do'
- = x 100000 Tong so dan so quan the do'd thdi gian
gida khodng thdi gian do'
Ty le thudng dupe tinh tren 100000 dan mot nam
8 Ty le chet/m ac.
Ty le chet/mac dupe tinh bang:
Tong so trUdng hpp chet vi mot benh nhat dinh mot thdi gian nhat dinh
- = x 100 Tong so trUdng hpp mac benh do' thdi gian do'
Ty le ndy bieu thi xac suat chet cua mot benh so nhdng trUdng hpp da dupe chan doan la cd mac benh, hay no bieu thi cho mdc nguy hiem cua benh Ty le chet/mac dupe sd dung dien hinh cac benh cap tinh, ty le it co' y nghia doi vdi benh man tinh bdi vi trUdng hpp benh man tinh thdi ky u benh cung nhu thdi ky mac benh keo dai va cd nhieu thay doi
Ty le chet/m ic cua cung mot benh thudng cung rat khac d cdc khu vuc khac
9 P h an tich , nhan dinh va sii du ng cac ty le.
Trudc phan tich, nhan dinh ve mot ty le, bao gib cung can lam ro nhung diem sau day:
(20)nao? Lieu nhung so co' dupe thu thap chinh xac khong?
- KhoAng thdi gian diin bien cua su kien (khoAng thdi gian thu thap so lieu) nen la khodng thdi gian nao? Cd hpp ly khong?
- Ty le lieu co' dem so sanh dupe khong?
- Ty le do' se duoc svi dung cho muc tieu nao? Co' phuc vu dupe cho muc tieu khong? Neu khong phan tich nhan dinh ky ludng trudc svi dung, co' the se mac phai nhung sai lam bien sau day:
+ Sai lam sit dung mau so khong dung:
Da co' khong it cac cuoc dieu tra quan tam den nguy co mac mot benh nao theo cac nho'm tuoi khac nhau, va lam mot bang tong hpp, thi du nhu sau:
N hom tuoi So mac Ty le phan trSm
DUrti tudi 1,8
1 - lufii 34 50,0
3 - tufti 16 23,5
5 - tuoi 10,3
10 - 14 tuoi
3 4,4
C ong 0 ,0
Va tii bAng tong hpp nay, neu di den nhan dinh rang nho'm 1-2 tuoi co' nguy co mac cao nhat la hoan toan khong chinh xac, vi ty le phan tram cl day chang qua chi bieu thi tan so mac cl cdc nho'm tuoi khac nhau, do' no' khong no'i gi dupe nguy co mac cua bat ky nho'm tuoi nao (TrUdng hpp phai tinh cac ty le mac rieng phan cua tung nho'm tuoi, bang cach chia so mac cua tilng nhom tuoi cho tong so ca the cua nhom tuoi quan the, mdi so sanh dupe, va mdi no'i len nguy co mac cua nho'm tuoi do')
+ Sai lam sit dung tit so khong dung:
Tinh tU so khong dung d i lam qua troi hoac qua non nguy co mac doi vdi mot benh Neu d i dang chap nhan tii so mot cach hdi hot, khong phan tich xem tOf so cd th at dung la so no'i len su kien can dieu tra nghien cUu khong, thi d i d in den ket luan sai lam nhu thi du sau day:
Thi du ngudi ta da tinh ty le chet ung thu d Philipin mot nam, rieng d vung nong thon thay 14,2.10 neu tinh cA d thi thi so len tdi 40,1.10"<i Co nen cho rang ty le chet ung thu d nong thon la thap khong? TrUdc nhan dinh ve van de nay, ngudi ta phAi phan tich den nhUng yeu to co the lam sai lam so chet thu thap dupe, nhu: d cd dieu kien chan doan tot hon, dan quan tam hieu biet vie benh tot hon, di kham chUa nhieu hon, de dang hon; so chet lai khong chia theo noi d cu ma chi ghi nhan vao sd chet d Them vao ho lai dupe ke la cd ho khau chinh thUc sau thang tam tru
+ Sai lam ve thdi gian da thu thap so lieu:
Muon so sanh dupe, cac ty le phAi dupe neu cung nhung thdi gian cd hoAn cAnh kinh te xa hoi, cd tien bo khoa khoe ky thuat nhu Dac biet luu y doi vdi cAc benh