I am assessing coping of father and mother by using Ways of Coping Questionnaire. I am using 2 domains of WoC ignoring other 6 domains though I have collected data for other domains too. As per my research question, I just wanted to test which coping style among the selected 2 widely used by mother and father and significant difference in their mean will tell. Though among all the domains the selected subscale mean were not greater than the other unselected one. So is it wrong to ignore other domain and use those two if can back up with the literature?
As long as all the scales have been collected, I see no threat to validity. You might want to use the other scales for exploratory analyses, however.
It is generally appropriate to focus on specific domains or subscales of a measure when addressing a specific research question, as long as the domains or subscales are relevant to the research question and are supported by the literature.
In your case, if your research question is focused on the coping styles of fathers and mothers, and the two domains of the Ways of Coping Questionnaire (WoCQ) that you have chosen are relevant to this question and are widely used in the literature, then it is reasonable to focus on these domains and ignore the other domains of the WoCQ.
However, it is important to consider the potential limitations of this approach. By ignoring the other domains of the WoCQ, you may be missing important information about the coping styles of fathers and mothers. Additionally, if the selected domains have lower means compared to the unselected domains, it is possible that these domains may not be as representative of the coping styles of fathers and mothers.
In general, it is important to carefully consider the appropriateness of the measures and domains that you are using in your study, and to ensure that they are well-supported by the literature and relevant to your research question. If you are able to provide evidence from the literature to support your decision to focus on specific domains of the WoCQ, this can help to strengthen the validity of your study.