anchor.diff:  
        <h2>Is the information in AACT up-to-date?</h2>
   
  -     <p>New content is downloaded from ClinicalTrials.gov and loaded into AACT every evening. These daily updates use the ClinicalTrials.gov RSS feed to identify studies that have recently been added or changed in ClinicalTrials.gov. New & modified studies are downloaded via the ClinicalTrials.gov API & loaded into AACT. Daily updates take anywhere from 20 minutes to several hours depending on how many studies have been added/changed. A full refresh of the AACT database will be run quarterly. The full-load takes approximately one day, during which time, the cloud-based version of AACT is not available. On the first of each month, a static copy of AACT is frozen and made available in 2 formats: 1) a PostgreSQL dump file and 2) a set of delimited text file. <a target='_blank' href='/snapshots'>Current and previous copies are available on the AACT website</a>, and may be useful for researchers seeking to run analyses off a static version of the database.</p>
  +     <p>The AACT database is updated every night at midnight, so the information in AACT is one day behind that which appears in ClinicalTrials.gov. The nightly update process uses the ClinicalTrials.gov RSS feed to identify studies that were added or changed in ClinicalTrials.gov the previous day, and then uses the ClinicalTrials.gov API to retrieve current data for just these studies. Only new/changed studies are created/modified. This process takes about one and a half hours, depending on how many studies were added/changed in ClinicalTrials.gov the previous day.</p>
  +     <p>Occassionally, studies must be removed from ClinicalTrials.gov, such as those that were accidentally entered twice. The nightly update process does not detect removed studies so once a month, the AACT database is dropped and completely refreshed.</p>
  +     <p>Both the nightly (incremental) and monthly (full) updates are performed on a 'background' database so that the publicly accessible database remains accessible while updates take place. When the process completes, the updated version is copied to the public database. This 'copy step' takes about 5 minutes, during which time the database is inaccessible. Since the nightly load starts at midnight and takes about one and a half hours, this 5-minute downtime usually occurs sometime between 1am & 2am.</p>
  +     <p>Please refer to the posted <a target='_blank' href='/update_policy'>update schedule</a> for more details.</p>
   
        <h2>How are unique studies identified in AACT?</h2>
   
  
positive.code:     <p>When interpreting this information, you’re encouraged to refer to the authoritative definitions provided by the National Library of Medicine (NLM). The most recent data element definitions are available on the NLM site for <a target='_blank' href='https://prsinfo.clinicaltrials.gov/definitions.html'>studies</a> and <a target='_blank' href='https://prsinfo.clinicaltrials.gov/results_definitions.html'>results</a> data. Data interpretation may depend on:</p>
      <ul class='regularDisplay'>
        <li><b>How the question was phrased.</b> For example, the definition of “Sponsor” does not necessarily imply that the sponsor is the agency paying for the clinical study, as might be expected from the common use of the term.</li>
        <li><b>Whether the respondent can enter a free-text answer to a specific question, or is restricted to a fixed set of possible responses.</b> Note that the definition of a data element and the available responses may have changed over time. The most recent data element definitions are available at the ClinicalTrials.gov site for <a target='_blank' href='https://prsinfo.clinicaltrials.gov/definitions.html'>study</a> and <a target='_blank' href='https://prsinfo.clinicaltrials.gov/results_definitions.html'>results</a> data. A history of changes through September 2011 for the study definitions can be viewed in the <a href="http://ctti-clinicaltrials.org/files/documents/AACTcomprehensiveDataDictionaryV3_2011.xlsx" download>AACT 2011 Data Dictionary</a>. Monthly copies of the AACT database are bundled with the data element definitions, AACT schema, and AACT data dictionary that were current at the time the copy was created.</li>
        <li><b>Whether there is dependence between fields.</b> Certain data elements need to be interpreted together with other data elements. For example, data elements such as enrollment date and completion date have a companion data element that indicates whether the value in the first field is an anticipated or actual value.</li>
      </ul>
  
  
negative.code: 
      <h2>How does content in AACT compare to what is in ClinicalTrials.gov?</h2>
  
      <p>AACT includes all protocol and results data for every study that is publicly available at ClinicalTrials.gov. All publicly available content from the current record for a study is included in AACT as it appears in ClinicalTrials.gov. The AACT database preserves the content from the source XML files downloaded from the ClinicalTrials.gov API; content is not cleaned or manipulated in any way. However, to help facilitate queries using AACT, several additional variables derived from the raw content are included in AACT's Calculated_Values table.</p>
      <p>The history of changes to a study record (available at the ClinicalTrials.gov archive site) is not included in the current version of AACT.</p>
  
      <h2>What types of questions can be investigated using ClinicalTrials.gov data?</h2>
  
  