Table 2 Methodologies' modifications taking into account prevalence-based analysis in cohort studies as base method

Variation respect prevalence-based analysis in cohort studies

Problem: Smoking prevalence is a poor proxy for cumulative hazards of smoking.

Solution: Defining SIR (Smoking impact ratio or Synthetic prevalence) authors avoid prevalence limitations.

Problem: RR extrapolation to different populations than the original is inconsistent.

Solution: Designing a case-control study OR could be assessed.

Problem: RR extrapolation to different populations than the original is inconsistent.

Solution: RR can be estimated applying a calculation procedure.

Calculation procedure

$SIR=\frac{C_{LC}-N_{LC}}{S_{LC}^{*}-N_{LC}^{*}}$

where C_LC, N_LC, S*_LC, N*_LC are age-sex specific lung cancer mortality rates for smokers and never smokers in the study and in the reference population (*).

$OR=\frac{a_1{b}_0}{a_0{b}_1}RR=\frac{a_1(1-p_1)}{a_0{p}_1}$

where

p₁ is the prevalence between the cases

a₁ is exposed cases

b₁ is exposed controls

a₀ is non exposed cases

b₀ is non exposed controls

Packs-function in smokers

RRs = 1 + ac((t - 5))-t₀)

Multistage-function in smokers

RRs = 1 + [(t - 5)^4.5 + ac(1 + 2ac)((t - 5)-t₀)^4.5 + 2ac((t - 5)^4.5-t₀ ^4.5)]/(t - 5)^4.5

Where a is a constant, c is the number of packs of cigarettes smoked per year, t is the current age and t ₀ is age at start of smoking.

In former smokers t₁ replaces (t - 5) and t₁ is age at stop smoking.