In 19xx the United States Food and Drug Administration (FDA) was created to "QUOTE".
As of Sept 2022 \todo{Check Date} they have approved 6,602 currently-marketed compounds with Structured Product Labels (SPL) 
and 10,983 previously-marketed SPLs. 
%from nsde table. Get number of unique application_nubmers_or_citations with most recent end date as null.
In 2007, they began requiring that drug developers register and publish clinical trials on \url{https://clinicaltrials.gov}.
This provides a public mechanism where clinical trial sponsors are responsible to explain
what they are trying to acheive and how it will be measured, as well as provide the public the ability to
search and find trials that they might enroll in.
Data such as this has become part of multiple datasets 
(e.g. the Cortellis Investigational Drugs dataset or the AACT dataset from the Clinical Trials Transformation Intiative) 
used to evaluate what drugs might be entering the market soon.
This brings up a question: can we use this public data on clinical trials to describe what effects their success or failure?
In this work, I use updates to records on \url{https://ClinicalTrials.gov} to disentangle 
the effect of participant enrollment and drugs on the market affect the success or failure of clinical trials.

%Describe how clinical trials fit into the drug development landscape and how they proceed
Clinical trials are a required part of drug development.
Not only does the FDA require that a series of clinical trials demonstrate sufficient safety and efficacy of
a novel pharmaceutical compound or device, producers of derivative medicines may be required to ensure that
their generic small molecule compound -- such as ibuprofen or levothyroxine -- matches the
performance of the originiator drug if delivery or dosage is changed.
For large molecule generics (termed biosimilars) such as Adalimumab
(Brand name Humira, with biosimilars Abrilada, Amjevita, Cyltezo, Hadlima, Hulio,
Hyrimoz, Idacio, Simlandi, Yuflyma, and Yusimry),
the biosimilars are required to prove they have similar efficacy and safety to the
reference drug.

When registering a clinical trial,
the investigators are required to 
% discuss how these are registered and what data is published.
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In the world of drug development, these trials are classified into different phases of development.
Pre-clinical studies may include 
Phase I trials are the first attempt to evaluate safety and efficacy in humans, and usually \todo{Describe trial phases, get citation}
Phase II trials typically \todo{}
A Phase III trial is the final trial befor approval by the FDA
Phase IV trials are used after approval to ensure safety and efficacy in the general populace ....

In the economics literature, most of the focus has been on evaluating how drug candidates transition between
different phases and then on to approval.

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