How to select one record from multiple record for a subject during analysis?

Question

I have a dataset where I am working on a binary classification. I have two classes of subjects. One is Outpatients and Other is Inpatients. (66:33 is the class proportion)

My objective is to identify the risk factors that influence hospital admission (Inpatients).

But the problem here is, I have my dataset like as below

1) Let's say we have a subject called "John". He has visited hospital 19 times based on my data duration from Jan 2001- Dec 2005. All of his 19 visits are outpatients.

2) Let's say we have another subject called "Jack". He has visited the hospital 34 times based on data duration from Jan 2001-Dec 2005. Out of 34 visits, he has been admitted as inpatient 18 times and rest 16 are outpatient visits.

So now my question is

1) Usually for analysis, we only see one record per subject/individual. Right? But now on what basis should I pick that one record?

Meaning, for John out of his 19 visits, which one should I pick?

Similarly for Jack, out of his 18 inpatient visits, which one should I pick?

I choose only one out of 18 from Jack because we don't need his outpatient info as we already have a separate group of outpatients and jack is considered for Inpatient class (because he has inpatient records too unlike John).

2) Is it really necessary to have only one record per person for analysis? Is there anyway to do this? Or is it like I have to represent in aggregate form the info of multiple records in one record? Is there any theory that allows analysis of multiple records for an individual?

Hope my question is clear and kindly request you to help me

Answer 1

I will try and be as concise as possible. First, let's redefine the way you think about your data points. There can ever only be two types of visits in terms of time. Periodic and Non-Periodic. Let's call each visit an event. Some events could be related to chronic conditions where periodic visits are quite common. Some events could be related to flu, head injury, etc., These are non-periodic visits. You need to think about what you are trying to predict. Are you predicting an inpatient visit based on periodic events or non-periodic events?

1) I would not recommend picking a single record in multiple visits as it is insufficient. For example, if I come in for a visit for a Blood Pressure Check-Up and you pick that event, then that means you only get that information but where as I would be visiting for a follow up check up or something like that or it could be pre-surgery visits. Some of these events could be both inpatient and outpatient depending on the nature of the event. It is also possible that some of the outpatient visits will lead to an inpatient visit. Jack's earlier outpatient visits could be a sign of him coming in as an inpatient. All of John's visits are outpatient but will he ever be an in-patient? Is that what are you trying to predict?

2) You can definitely have multiple records per person and treat them as a sequence of visits over a period of time. This basically means that you are treating these visits as sequences. Most of the health care related risk prediction stuff is based on sequences. It is just the way you treat sentences. Each patient is described by a sentence of visits. This meaning, you can leave John's visits and Jack's visits as they are and use padding techniques to make them appropriate for a deep learning solution to classify which one would be inpatient.

You can refer to this paper.

This is definitely not concise but the number of permutations and combinations when it comes to healthcare stuff is high. Please let me know if you've got any questions.