Risk factors and immunological pathways for asthma and other allergic diseases in children: background and methodology of a longitudinal study in a large urban center in Northeastern Brazil (Salvador-SCAALA study)

Table 1 Estimation of the sample size and power of the study

					Assuming study power of 80%
Risk factors (all categorical values: 1 = exposed, 0 = not exposed)	Number of children with data on the risk factor		Proportion exposed (risk factor = 1)	Estimated number with asthma	Estimated prevalence in:		PRR⁴
	n	90%			not exposed	exposed
(a)	(b)	(c)¹	(d)	(e)²	(f)	(g)	(i)
Measles vaccination (unvaccinated over vaccinated)	1,407	1,266	0.75	126	0.08³	0.15	1.7
Maternal smoking during pregnancy (smoker over non-smoker)	1,412	1,271	0.14	127	0.09	0.17	1.9
Sanitation connection	1,409	1,268	0.52	127	0.07	0.13	1.7
Maternal schooling (illiterate and primary over higher schooling)	1,441	1,296	0.76	130	0.05	0.11	2.0

1-assuming a loss rate of 10% for the survey in 2005, it is (b) multiplied by 0.9;
2-assuming a asthma prevalence of 10%, it is (c) multiplied by 0.1;
3- unvaccinated;
4- prevalence rate ratio.

ISSN: 1471-2466