What would you do if you are in an advisory role with 80-90% right decisions, but your manager makes up a wrong decision?

forecast the results of the wrong decision before the manager.
statsitically report the outcome of the wrong decision to the manager.
if the decision is still on ! be bold to call a meeting of the heads and Allow yoyurself a chance to propose the big suggestions to heads alongwith a chance for the manager to explain his/her point to the higher authority.

Advisor shall prepare a report of his opinion but this report shall include all the evidences supporting his point of view (evidences include statistical analysis of the situation, supporting reports from similar situations and any other means necessary to convince his manager of his point) then send it to his manager with asking of meeting to discuss the report.
If the manager insist on his situation then the advisor shall normally raise the report to the manager's boss to clear your area and clarify the image to the top management

One should professionaly convince his manager to take the right decision.
As at the end of the day, its the Organization, which will prosper or suffer with right or worng decisions, respectively.
Advisor should explain his manager about the results of this decision and eleborate him, how its going to effect the Organization.
As per US management ethics, still if the manager compels to carry on the same wrong decision, which going to damage the business.Then it becomes the ethical responsibility of the subordinate to inform the situation to the supervisor of his manager.

In the UK where I live and have worked for many years within the HR field, the employment relationship is governed by employment legislations and should be adhered to by everyone, including managers. It is their responsibility to ensure they do not bring the reputation of the organisation into disrupt by their wrong decision or failure to be seen not to follow the policies and guideline as laid down by law. Employees or members of the public who feel they have been treated unlawfully can bring a claim of discrimination against an organisation whether they are employees or not, therefore managers have a responsibility to ensure that their behaviour and attitude does not come across as been discriminatory.

 

Managers as leaders have to also follow the laws as lay down by legislations, company policies and good practice and must be seen to act in a way that shows they are leading by example. However the fact that there are laws does not stop some managers from trying to make wrong decisions that are based merely on their personal opinion or feelings. If I am aware that my manager or any manager within my organisation is going to make a wrong decision that is based on their personal feeling or against the law, it will be my responsibility as the HR professional to inform them why it should not be done. I will point them to the policy that says there is another way of managing the situation, including the outcome and implication of what will happen if their decision is carried out. In HR we try to work to ensure best practice as stipulated within the CIPD Code of Professional Conduct and it is our duty to ensure managers do the same as this will be a consideration when a case goes to an employment tribunal.