Letter to editor about the article "Do psychiatric patients experience more psychiatric symptoms during COVID-19 pandemic and lockdown? A case-control study with service and research implications for immunopsychiatry" (Hao et al., 2020).

Dear editor,

In your journal from April the article “Do psychiatric patients experience more psychiatric symptoms during COVID-19 pandemic and lockdown? A case-control study with service and research implications for immunopsychiatry”, Hao et al. (Hao, et al., 2020) reported an increase in the stress and psychological impact experienced by people with ut psychiatric illnesses, compared to a control group during the peak of 2019 coronavirus disease (COVID-19) epidemic. Although the important issue raised in the paper because mental disorders have increased with the pandemic (Yao et al., 2020), issues in the design of the study may have hammed the conclusions.

Case control studies may be trick mainly in the definition of the control group and in the Hao publication definition of controls have problems: 1) response rate to the questionnaire among case was 11·3% and 83·8% in the control group; 2) there is no description of clinics or mechanism to find controls. It is described as a convenience sample; 3) “the inclusion criteria were different for psychiatric patients and healthy controls”, without explanation.

Results from case-control studies should be as in table 2 a comparison of exposure between these groups. However, authors further compare by linear regression analysis psychological impact and self-reported health status and history of psychiatric illnesses in all respondents, with adjustment to demographic factors. Therefore, we really do not know how much of the results are related to inadequate analysis and selection bias of the participants.

By the way percentages in the table for sex and others are wrong.