Selection: (Maximum of 5 stars)

1) Sample representativeness:

a) Truly representative of the mean in the target population.* (All subjects or random sampling)

b) Slightly representative of the mean in the target population.* (Non-random sampling)

c) Selected group of users.

d) Description of the sampling strategy.

2) Sample size:

a) Justified and satisfactory.*

b) Not justified.

3) No answers:

a) The comparability between responses and non-responses is established – and the response rate is satisfactory.*

b) The response rate is not satisfactory, or the comparability between responses and non-respondents is unsatisfactory.

c) Description of response rate or characteristics of responses and non-responses.

4) Exposure calculation (risk factor):

a) Validated measurement tool.**

b) The measuring tool is not validated, but the tool is available or described.*

c) Description of the measuring tool.

Comparability: (Maximum of 2 stars)

1) The objects in different result groups are comparable, based on the study design or analysis. Confounding factors are controlled.

a) The study takes into account the most important factor (select one). *

b) Study control for any additional factor.*

Result: (Maximum of 3 stars)

1) Evaluation of results:

a) independent blind evaluation.**

b) Record association.**

c) Study's own report.*

d) no description.

2) Statistical test:

a) The statistical test used to analyze the data are clearly described and adequate, and association measurement is shown, including confidence intervals and the level of probability (p-value).*

b) The statistical test is not appropriate, not described or incomplete.

This scale was adapted from the Newcastle–Ottawa Quality Assessment Scale for cohort studies to perform an evaluation of cross-sectional quality studies for the systematic review, “Are healthcare workers’ intentions to vaccinate related to their knowledge, beliefs and attitudes? A systematic review”.