The overall process of decision making in staff selection includes the following stages:

1. Identifying the need for a new member of staff:
This stage involves recognizing the requirement for an additional staff member within an organization. It may be due to increased workload, expansion of business operations, or filling a vacant position.

2. Agreeing the job specification:
Once the need for a new staff member is identified, the next step is to define the job specification. This involves determining the specific responsibilities, qualifications, skills, and experience required for the position.

3. Advertising the job:
After agreeing on the job specification, the organization advertises the job opening to attract potential candidates. This can be done through various channels such as online job portals, newspapers, or recruitment agencies.

4. Receiving and reviewing applications:
In this stage, the organization receives applications from interested candidates and reviews them based on the job requirements. The review process involves assessing the qualifications, skills, and experience of each applicant to shortlist potential candidates for further evaluation.

5. Conducting interviews:
The shortlisted candidates are invited for interviews, which can be conducted in various formats such as face-to-face interviews, telephonic interviews, or video interviews. The purpose of the interview is to assess the candidate's suitability for the role, their communication skills, and their ability to handle job-specific tasks.

6. Assessing candidates through tests and assessments:
In addition to interviews, organizations may also use tests and assessments to evaluate the candidates further. These assessments can include aptitude tests, personality assessments, or practical tasks relevant to the job role.

7. Making the final decision:
After completing the interview and assessment process, the organization evaluates all the information gathered on each candidate and makes the final decision. This involves comparing the qualifications, skills, experience, and overall fit of each candidate against the job requirements and organizational culture.

8. Deciding which candidate to appoint:
The last stage of the decision-making process in staff selection is selecting the most suitable candidate for the job. The decision is based on the evaluation of the candidate's performance in the interviews, assessments, and their overall fit with the organization's requirements.

In conclusion, the overall process of decision making in staff selection includes identifying the need for a new staff member, agreeing on the job specification, advertising the job, reviewing applications, conducting interviews, assessing candidates through tests and assessments, making the final decision, and ultimately deciding which candidate to appoint.