Estimating the percentage of a specific factor being related to a condition I am working on a medical research project where I am trying to find the associations between specific maternal factors and neonatal limb ischemia (NLI) to declare the maternal factors as "risk factors for NLI". I am trying to find a way to estimate the percentage of a specific maternal factor being associated with NLI, but I am having a hard time figuring out how to make the estimates.
The data is only on NLI patients. In terms of associations between maternal factors and NLI, the factors include maternal health problems, maternal age, maternal ethnicity, previous pregnancies and births, and maternal substance use (smoking, drinking, drug use, medications).
I have a bit of a background in stats, but I am not sure what the best way is to calculate the estimates. I have a lot of data of 120 patient cases from around the world retrieved from papers. I have made an Excel of all the relevant information regarding each patient. The data is not perfect since it all comes from different papers, but I've tried to make an Excel where the information is organized in a consistent manner. I have an idea of what trends seem to show within my data sample but I don't know how to validate these trends by conducting an estimate.
I have tried to think of ways to do the estimate, but I am not a stats expert. I thought that clustering might be helpful here to group the data, but I'm not sure what to do with the groups and if clustering would even help develop the estimate of the percentage. I am also still learning how to cluster, so I am hesitant to go this way.
Are there any suggestions for simple techniques I should employ for the estimate?
 A: Without data on situations without NLI, you won't be able to answer your question adequately.
For a trivial but important example of the problem with evaluating maternal factors just within NLI data: all mothers of your NLI cases were females. That would be the strongest association with NLI in your data set, even though it's also true of all births without NLI.
Even if you found clusters of less-trivial maternal factors within the NLI cases, you wouldn't know whether those clustered similarly in births without NLI. At the least, you need to find some distributions of values in normal cases for comparison.
Then you could try to examine whether the distribution of one or more maternal factors among NLI cases differs from that in normal cases, although the multi-cultural distribution of NLI cases in your data set will even make that a challenge. You would probably need to find normal cases with the same geographic distribution as your NLI cases.
That said, there's nothing wrong with presenting a summary of multiple case reports as you seem to have accumulated, including the distributions and associations of maternal factors in your data. On that basis alone, however, you can't call those "risk factors for NLI."
