L4 Meas dis in pops

Question 1

LO2: imp of systemat var in risk of dis btw diff grps: as usef source or dis cause, as nuisance which needs contr for.

Answer 1

-usef vars in risk of dis eg RFs. sys vars/non rand in risk btw peop clues about aetiol. sep sing grp survey from compar.
-aetiol- comp levs of expos in 2 grps and try ID causal fac.
contr grp=
id ID can prev expos and decr incid.
-IRR=rateb(exposed)/ratea(unexp). incid higher in exp sugg assoc with rate of dis.
-efficacy- IRR comp effs of 2 tx. old tx/new. IRR 0.5=new tx halves risk of death.
rate meas absol risk. ratio relative risk.
-as a nuisance- eg age and sex. rate old/yng us over 1.not modifiable so less usef for preven. confoundign can expl all/part of assoc btw expos and dis.
if age specif RRs get lot res diffic interp.

Question 2

LO3: expl purp of age-sex stand.

Answer 2

• what would RR for 2 grps be if age-sex stuc was same. stand mort ratio calc. want sing overall RR accs for systemat var.

Question 3

LO4: interp a stand mortal/morbid ratio (SMR).

Answer 3

• SMR is summ fig comparing: lev of mort/morb OBS in study pop with lev EXPEC if stand ref pop age-sex specif RRs were applied to study pops age-sex grps. accs for age-sex confounding.
• SMR us exp as %. 100=same risk in study pop as stand ref. more than 100=higher risk in study pop. 200=2x likely. can be exp rel to 1.

Question 4

LO1: def and diff btw incid and preval. desc interels and changing patts of death and cure.

Answer 4

-incid- no new cases that occ. usef in monit epidem. incls time eg no peop out of pop per yr. indiv risk. pop av risk, but not all indivs same risk, vary btw grps.
incid rate=new events/personxtime(yr)=events per person yrs eg mort rate.
imp to see if cases incr freq, eff of prevention, comp those exposed to an RF vs not, us ST dis.
-preval- no peop aff by dis. all exist dis old and new. descs burden. usef meas need for services, us stable, LT cond. just a propor. study is x sec survey no foll up. pt vs period. if had infec dis multip times counts as 1.
preval tells burden. need for dervices. lifelong conds. this is pt preval=suffs/at risk.
- rels- incr incid=incr preval if death and cure rate same. incr cure=decr preval. incr death=decr preval. incr surv time=incr preval.
preval approx=incidx length of dis.