Question

A study investigated bladder disease and laxative use in men between 80 and 89 years old. There were 3000 current laxative users and 7000 laxative non-users at baseline. Within 7 years, 12 of the laxative users and 6 of the laxative non-users developed bladder disease

1. What kind of study is this?

2. What if you want to test the hypothesis that the odds ratio is equal to one. The 95% CI is (1.27, 8.56). What is the conclusion?

3. Now the hypothesis is tested that the risk of bladder disease is 1 in each group (laxatives and non laxatives). Write alternative&null hypothesis (please also define parameters).

Answer 1

1) As we have two groups - one group using laxative (exposed group) and other non - laxative users (unexposed group) and they are followed up for 7 years to see whether they develop bladder disease or not. So, it is a prospective study where we are moving from cause to effect. Hence, it is a cohort study.

2) As 95% CI of odds ratio = [1.27, 8.56], that is both the lower bound and upper bound are greater than one, so, it doesn't include the null hypothesed value of the odds ratio (I e, one), hence, we conclude that the odds ratio is greater than one. Hence, the exposure is the risk factor for outcome.

3) Null hypothesis (Ho) : The Risk of developing the bladder disease among laxative users is same as risk of developing the bladder disease in laxative non-users.

i.e, Relative Risk (R.R) = 1

Alternative hypothesis (H1) : The risk of developing bladder disease among laxative users is higher than the risk in the laxative non-users.

i.e, R.R > 1

Parameter is Relative Risk (R.R) which is the ratio probability of developing disease (incidence of diseases) in exposed group to the probability of developing disease (incidence of disease) in non exposed group.

If R.R = 1, it means exposure has no effect on outcome (disease).

If R.R > 1, it means that exposure is the risk factor for outcome (disease).

If R.R < 1, it means that the exposure is the protective factor for outcome (disease).

	Having bladder disease	not having bladder disease	Total
Laxative users	a = 12	b = 2988	a+b = 3000
Non laxative users	c = 6	d = 6994	c+d = 7000
Total	a+c = 18	b+d = 9982	N = 10,000

So,

Since, R.R > 1, laxative use is risk factor for the bladder disease.