Documentation page on survey problems

docs/symptom-survey/problems.md

@@ -0,0 +1,75 @@
+---
+title: Problems and Data Errors
+parent: COVID Symptom Survey
+nav_order: 7
+---
+
+# Problems and Data Errors
+{: no_toc}
+
+Given the scale of the COVID Symptom Survey, we occasionally encounter data
+errors or survey implementation problems that affect the interpretation of
+results. All problems will be logged here.
+
+## Table of contents
+{: .no_toc .text-delta}
+
+1. TOC
+{:toc}
+
+## Election-Related Sample Size Decreases (Nov 2020)
+
+Sample sizes decreased in the days following the 2020 US presidential election.
+During this time period, Facebook prioritized providing users with
+election-related information, which led to fewer people seeing invitations to
+the survey. Sample sizes returned to their pre-election baselines in mid-to-late
+November.
+
+## Missing Item C15 in Data Files (Nov 18, 2020)
+
+In [Wave 4](coding.md), we added item C15, which asks respondents "How worried
+are you about your household's finances for the next month?" Unfortunately, our
+code that produces the [individual data files](survey-files.md) inadvertently
+omitted this item.
+
+We've now corrected this problem and reissued the data files that include
+Wave 4. If you have access to the SFTP server containing microdata, you'll find
+new response files with names such as
+
+    cvid_responses_2020_10_31_recordedby_2020_11_16.csv.gz
+
+where "recorded by 2020-11-16" means they were issued on November 16th. Older
+versions with prior "recordedby" dates were created before this mistake was
+corrected.
+
+The monthly data files, with names such as 2020-11.csv.gz, use the reissued data
+and are not affected by this problem.
+
+## Unintended Highlighted Answer Choices (Feb 19, 2021)
+
+Some respondents reported that certain multiple-choice questions displayed the
+first response option highlighted in red. This occurred when a matrix-table
+question is followed by a single-choice question. This problem only affected
+respondents completing the survey on mobile devices; after completing the last
+item in the matrix table question, Qualtrics automatically moved them to the
+single-choice question and highlighted the first answer choice.
+
+We have put in page breaks after the matrix-table questions that have seem to
+resolve the issue. However, data collected before the problem was fixed may be
+biased by the highlighting of the answer choice.
+
+Listed below are the survey waves and items that were possibly affected:
+
+* Wave 8 from February 8, 2021 – February 19, 2021:
+  * Item V9 (How concerned are you that you would experience a side effect from
+    a COVID-19 vaccination?)
+  * Item C9 (How worried do you feel that you or someone in your immediate
+    family might become seriously ill from COVID-19?)
+* Wave 7 from January 12, 2021 – January 28, 2021:
+  * Item V9 (How concerned are you that you would experience a side effect from
+    a COVID-19 vaccination?)
+  * Item C9 (How worried do you feel that you or someone in your immediate
+    family might become seriously ill from COVID-19?)
+* Waves 1, 4, 5, and 6:
+  * Item C9 (How worried do you feel that you or someone in your immediate
+    family might become seriously ill from COVID-19?)

docs/symptom-survey/survey-files.md

@@ -18,7 +18,8 @@ access to the individual survey responses. If you have not done so, aggregate da
 
 Important updates for data users, including corrections to data or updates on
 data processing delays, are posted as `OUTAGES.txt` in the SFTP server directory
-where the data is hosted.
+where the data is hosted. Our documentation on [data errors](problems.md)
+explains any issues that may affect your use or interpretation of this data.
 
 ## Table of contents
 {: .no_toc .text-delta}