@@ -17,6 +17,50 @@ interpretation of results. All problems will be logged here.
17171 . TOC
1818{: toc }
1919
20+ ## Incorrect Wave Sampling (June-August, 2021)
21+
22+ A sampling error caused a portion of our respondents to be accidentally sent the
23+ Wave 10 survey instrument instead of the newer Wave 11 survey instrument. The
24+ error was fixed on August 2, 2021, but as a result of this error:
25+
26+ * A random 1% of the sample was accidentally sent the W10 instrument between
27+ June 15 and July 4, 2021.
28+ * A random 3% of the sample was accidentally sent the W10 instrument between
29+ July 5 and July 11, 2021.
30+ * A random 10% of the sample was accidentally sent the W10 instrument between
31+ July 12 and July 21, 2021.
32+ * A random 50% of the sample was accidentally sent the W10 instrument between
33+ July 22 and July 30, 2021.
34+ * A random 91-98% of the sample was accidentally sent the W10 instrument between
35+ July 31 and August 1, 2021.
36+
37+ Despite differences between the two instruments, we have not detected trend
38+ discontinuities as a result of the error. We will continue to investigate.
39+
40+ ## Response Volume Drop (July 20-22, 2021)
41+
42+ On July 20, 2021, a technical problem in the process that samples Facebook users
43+ for invitation to the survey caused lower-than-normal sample sizes. The problem
44+ was resolved on July 22 and users that had been incorrectly not invited were
45+ invited over the following several days. This caused sample sizes to temporarily
46+ increase, compensating for the initial drop.
47+
48+ ## Android Sampling Problem (June 17-24, 2021)
49+
50+ There was a bug in the in-app web browser in the Android version of the Facebook
51+ app released on June 17. It affected all links within the Android version of the
52+ Facebook app, not just the Carnegie Mellon University (CMU) and University of
53+ Maryland (UMD) COVID-19 Trends and Impact Surveys, which are conducted in
54+ partnership with Facebook. It did not affect links within other versions of
55+ Facebook, including iOS. The issue has been fixed in the version of the Facebook
56+ app released on June 24.
57+
58+ The issue caused a decrease in total response volume across the CMU and Maryland
59+ surveys, since Android users who were invited could not take the surveys. As of
60+ June 26, 2021, 89.5% of the initial decrease in total response volume has been
61+ recovered. The response volume continued to recover as Android users updated to
62+ the fixed version of the Facebook app.
63+
2064## Incorrect Coding in Documentation
2165
2266We found a Qualtrics bug that affects the exported text of the survey (but not
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