To control for possible confounding effects of physical illness other than COPD, we retrieved data on previous hospitalisation for other physical illness from the NPR, excluding pregnancy and childbirth, mental and behavioural disorders and external causes (including accidental and intentional poisonings, and injuries), prior to the time of suicide or the matching date of control (index date).
In some articles (Hepworth et al. 2006; Schoemaker et al. 2005), controls were allocated into categories of interview lag time at random without consideration of age and sex of the cases within these categories, whereas in others (Lönn et al. 2004a), average lag between diagnosis and identification in a matched set was subtracted from date of control identification.
All contemporary factors were asked of cases up to or around diagnosis date and of controls, up to the date of interview.
The risk factor status of both cases and controls was updated from the questionnaire most recently completed before date of diagnosis (controls were assigned the date of diagnosis of their matched case).
Cases were matched to surgeon, gender, body mass index, age, and date of surgery controls (n = 20) who underwent primary unilateral TKA without developing VTE before patient discharge.
The index date of the controls was set to be that of the case (i.e. the start of the exacerbation episode).
The index hospitalization date of the controls was limited to be within the same year as that of their matched cases.
The difference in average date of participation (controls) vs. average date of diagnosis (cases), which determined when exposure assessment ceased, was less than 6 months (Table 3). 1 cumulative exposure on transformed ratings: 1 (low), 2 (moderate), 3 (high) → 0, 10 10, as rating-year.
The index date of the control patients was randomly assigned based on the distribution of index dates of SLE patients.
The reference date for control patients was determined by adding the hospitalised period of the matched CDI patient (time between admission and start of diarrhoea) to the admission date of the control patient.
