biostatistics for ordinal variable

#1
The study is perspective.
the subject is : the effect of an intervention on antibiogram level



I will have a antibiogram value at (4: for clean- 3 for a few- 2 for moderate and 1 for many bacteria) for each patient( 5 patient in every group, 10 patient in control and intervention groip).
and i have collected antio biogram for 4 time, base, after 10 days, after 20 days, after 30 days.
______

Question

My question is: how can I statistically assess whether or not there is a significant difference in the (hypothesised) antibiogram from base to 30 day between the study group and the control group, and which type of analysis and test come into play?
thank you so musch
 
#2
You want a nonlinear multilevel model. "Nonlinear" because your dependent variable is ordinal, not continuous and "multilevel" because you have repeated measures and, therefore, violate the assumption of independence. These are complex models. They are available in SAS (GLIMMIX or NLMIXED) and R (nlme) and possibly other packages.
 

Karabiner

TS Contributor
#4
At each time point you could determine whether antibiogram value
has improved compared to baseline, and then compare the new variable
("improvement yes/no") between groups usin Chi2 or Fisher's test.

With kind regard

K.
 

Karabiner

TS Contributor
#6
i do this , but i have a problem, my antibiogram level has 4 status, many- mod- a few- cleam!!!
Where exactly is the problem, then? You can tell, for every
single case, whether there was a change from baseline or not.

If patients were randomized into the respective groups,
you could alternatively just perform an U-test at each time
point (analysing the original dependent variable).

With kind regards

K.
 
#7
the problem is here: if someone is clean at base because of antibiotic usage then after cut of antibiotic and doing our intervention , again the antibiogram is clean . what should we name this event?
 

Karabiner

TS Contributor
#9
the problem is here: if someone is clean at base because of antibiotic usage then after cut of antibiotic and doing our intervention , again the antibiogram is clean . what should we name this event?
Unchanged. Or perhaps you should have inclusion criteria
for study subjects, such as: only subjects are included who
were un-clean at baseline. But such considerations depend
on substantial knowledge in the field, which I don't have.
the antibiogram has 4 level and sometimes the level is constant but it means it has an improvement
Again, what you consider a success depends on your own knowledge
and research interests.

With kind regards

K.
 

Karabiner

TS Contributor
#11
I see. So, at baseline, all partcipants have value "4"?
You can compare groups at each time point using a
U-test, then.

With kind regards

K.