# Basic Questions regarding Long-COVID from COVID Symptom Study app

The study Attributes and predictors of Long-COVID: analysis of COVID cases and their symptoms collected by the Covid Symptoms Study App is a prospective observational cohort study of COVID-19 symptoms in a subset of 4182 users of the COVID Symptom Study app meeting inclusion criteria.

Briefly, the subset comprised individuals

• who had tested positive for SARS-CoV2 by PCR swab testing
• who logged as “feeling physically normal” before the start of illness (up to 14d ays before testing) so that we could determine onset.

From Table 1. "Characteristics of COVID-19 by duration of symptoms" contains values in brackets() and i would like to know what they mean

``````            |   A       |    B      |     C     |     D     |
| Overall   |   Short   |   LC28    |    LC56   | Remark
Number      |  4182     |   1591    |    558    |    189    | A-B-C-D = 1844 question 7
Age (years) | 42.8(13.4)| 40.1(13.6)| 48.9(12.7)| 50.9(12.5)| questions 1 to 3
BMI         | 27.3(5.9) | 26.8(5.7) | 27.5(5.7) | 27.5(5.8) | question 4
``````

Questions 5 and 6 concerns line 111:

Cardiac symptoms (palpitations, tachycardia) were over-represented in the LC28 group (6.1%) compared to in short-COVID (0.5%) (p<0.0005)

My understanding (Q5, Q6)

• I assume that p stand for p-value. According to exclusions of null hypothesis (often denoted H0) the null hypothesis is a default hypothesis that there is no difference between two measured phenomena.

• If `H0` is the hypothesis that there is no correlation between cardiac symptoms among short-covid compared to LC28 than the likelihood / probability of this hypothesis is very low (0.0005)?

Questions

1. Row `Age (years)` What does `42.8 (13.4)` mean - is 42.8 the median age and 13.4 Interquartile range (IQR) from 25% to 75%?
2. If `13.4` is the IQR does that mean the lower boundary (25%) age is 29.4 years `(42.8 - 13.4)` or 36.1 years `(42.8 - (13.4/2))`?
3. If `42.8 (13.4)` means something different could you explain?
4. Row `BMI` What does `27.5(5.8)` mean regarding body mass index?
5. Does `(p<0.0005)` mean the p-value (likelyhood) for no correlation?
6. Is my understanding correct?
7. Does anyone know what is up with the delta of 1844 persons? Are they without symptoms?