BMI and Diabetes in Ramallah, Answers Presentation Hein Stigum H.S.

Exercise 1 Design: Tverrsnitt Prevalens: Få eldre  underestimering (overskrift “diabetes”?) Assosiasjon: RD, RR, OR (CaseContr: bare OR) Risikoen for diabetes er 2.4 ganger høyere blant de fete d) Oddsen for diabetes er 2.7 ganger høyere blant de fete H.S.

e) Feilkilder 3 feilkilder: Seleksjon, Informasjon, Konfundering Diabetes BMI age + 1 biased true 2.4 Positive bias Selection: too few old->underestimation Information: BMI underreported Confounding: Other factors: Sex Physical activity Genes Konfundering kan justeres vekk i regresjonsmodeller 13. okt. H.S. H.S. 3

Oppgave 2 “Truth” Spesifriskitet Low Sensitivity or Sensitivity PPV and NPV depend on prevalence Multiply left column by k to see Spesifriskitet Low Sensitivity or Sensitivity Research: Information bias Screening: → Clinic: H.S.

Oppgave 3 Spørsmål Valid Reliabelt Hvor høy er du (m)? ja ja Spiser du sundt? nei ja Enheter alkohol siste 30 dager ja nei Hva er din BMI? nei nei H.S.

Design decision elements H.S.

Time E,D no time cross-section E → D prospective cohort, nested CC, Case-Cohort E ← D retrospective traditional CaseControl Present time Oct-17 H.S.

3 Main Designs Cross-section Cohort Traditional Case Control D+ D- E+ No time Fast Reverse Causality E- D+ D- Cohort E+ Prospective Reliable Size Time E- D+ D- Traditional Case Control E+ Retrospective Efficient for rare disease Recall bias Sampling of controls E- H.S.

Design decision elements 1) Rare disease 2) Reverse causation Cross-section (E,D same time) Sex  Smoke no Diet  Cancer yes Sugar  Caries maybe H.S.

Design decision elements 3) Latency Cohort (follow from E to D) Smoke  Cancer 20-40 years Sugar  Caries 2-6 months Norwalk  Vomit 1-3 days 4) Recall bias Case-Control (ask for D back in time) Alcohol  Cancer poor recall Sex debut age  HPV good recall H.S.

Design decision elements Rare disease excludes cross section and cohort Reverse causation excludes cross section Long Latency excludes cohort Recall bias excludes case control H.S.

Design Flow Chart Rare disease no yes Reverse causality Long latency Recall bias yes yes yes Alterative group no no no Flow chart: not perfect. Real life designs often compromises and often with twists. Design choice if often by exclusion. Alt group: diabetes is rare in population, but more common in relatives of diabetic subjects. Cross- section Cohort Case Control H.S.

Design decision elements 3 Alternative study group If cancer is rare  study old If diabetes-2 is rare  study Pakistani If diabetes-1 is rare  study 1. grade relatives H.S.

Oppg 4: Sukker og karies Kohort Siden 1995 har 12-åringene i gjennomsnitt hatt under 2 tenner med kariesangrep. I 1985 var tallet cirka 3,5 tenner (SSB). Tilnærmet insidens: 0.50*2/12=0.08 nye hull per person år Forekomst: ikke sjelden sykdom Revers kausalitet: ja kanskje Kohort Lang latenstid: nei (2-6 mnd) Recall bias: ja kanskje H.S.

Sukker og karies H.S.

Prevalens=Insidens*Tid_syk Oppgave 5 Ved steady state: Prevalens=Insidens*Tid_syk H.S.

Evaluering H.S.