Hello Stephanie ,,,

If you need to measure incidence ( sample be taken as 2 groups : exposed and non-exposed ) ,,, to follow up and detect new event.

If you need to measure prevalence and was one group then classified after data collection ,,, it will be multi-stage cross sectional survey.

Survey generally is = Cross sectional when population based.

Regarding : G*power app ... You have to wait ana answer from an expert.

Thanks.

Thank you for your answer. My study sounds more like the second you described; measuring prevalence using the same sample group over a period of time.

In my experience I thought a cross sectional design was when you use two different groups. Is this not correct? Would this be considered a longitudinal study?

yes it is called comparative cross sectional study if researcher begins with 2 different groups.

In your study case the 2 different groups are taken from same sample ( members of a wellness center ) so it will be Longitudinal studies that differ from one-off, or cross-sectional, studies. The main difference is that cross-sectional studies interview a fresh sample of people each time they are carried out, whereas longitudinal studies follow the same sample of people over time.

Also please check the table attached.

source : https://learning.closer.ac.uk/introduction/types-of-longitudinal-research/longitudinal-versus-cross-sectional-studies/

===========================

please note

Indian J Dermatol. 2017 May-Jun; 62(3): 321. doi: 10.4103/0019-5154.206187PMCID: PMC5448271PMID: 28584379

Descriptive versus Analytical Studies in a Clinical Setup

The epidemiologic studies are either descriptive or analytical studies. Descriptive studies include case reports, case series reports, cross-sectional studies, surveillance studies, and ecological studies whereas analytical studies are either experimental or observational. Case–control and cohort studies are the type of observational studies out of which the latter is usually the prospective study.[2]

Hence, how can a study be “cross-sectional, i.e., descriptive” and “prospective” at the same time?

They have recruited a total of 100 consecutive patients, newly diagnosed as acne vulgaris, of age 15 years and above in the study. Hence, this is a cross-sectional study which gives the snapshot of the situation for the particular period. In a cross-sectional study, the investigator measures the outcome and the exposures in the study participants at the same time.[3] However, in a cohort study (written prospective in this article), the participants do not have the outcome of interest to begin with. They are selected based on the exposure status (acne vulgaris) of the individual. They are then followed over time to evaluate for the occurrence of the outcome of interest (psychosocial in the present article).[4]

references:-

2. Kaushal K. Quality of life and psychological morbidity in vitiligo patients: A study in a teaching hospital from North-East India. Indian J Dermatol. 2015;60:512.

3. Setia MS. Methodology series module 3: Cross-sectional studies. Indian J Dermatol. 2016;61:261–4.

4. Setia MS. Methodology series module 1: Cohort studies. Indian J Dermatol. 2016;61:21–5.

Cross sectional can be descriptive or analytic according to purpose. And in your case it will be analytic ( 2 * 2 table ) and you have to check also hints like meaning of design effect when calculating sample size ( according to the method of sampling).

Power analysis for cross-sectional and longitudinal study designs

• DOI:10.3969/j.issn.1002-0829.2013.04.009 in attached file

=====================

How can I calculate design effect in a prevalence study with multistage random sampling?

https://www.researchgate.net/post/How_can_I_calculate_design_effect_in_a_prevalence_study_with_multistage_random_sampling

What is Design Effect?

https://www.researchgate.net/post/What_is_Design_Effect

How can one determine the sample size in multistage cluster sampling?

https://www.researchgate.net/post/How_can_one_determine_the_sample_size_in_multistage_cluster_sampling