Barely a week goes by without another controversy hitting the country's single police force.

On Thursday, Assistant Chief Constable Bernie Higgins told MSPs that armed officers had "engaged with the public" on 1,644 occasions since October.

This was in spite of earlier assurances by Chief Constable Stephen House that officers would not be armed when dealing with routine incidents.

This apparent contradiction will result in senior officers being recalled to Parliament.

It has now emerged that the internal Police Scotland survey which shows high satisfaction levels with the service is also questionable.

Between January and December 2013, around 16,000 people took part in "user" interviews that produced satisfaction scores of around 80% amongst the public.

However, the respondents are only those people who have reported crimes or incidents to the police.

Excluded are individuals who have been stop searched - there were over 600,000 frisks recorded in 2013/14 - suspects and motorists who have been pulled over.

Put simply, the group most likely to be happy with the police is the same group to have been sampled.

The exercise looks less like an impartial study based on rigorous methodology and more like a 'rigged' series of interviews designed to get the right result.

The HM Inspectorate of Constabulary shares some of the concerns about the in-house sampling. In a report on local policing last month, HMIC states:

"We acknowledge that every effort is made to ensure the integrity of the process but in the interest of transparency we are of the view that independent surveys may provide a better means of obtaining valid and reliable levels of satisfaction and confidence."

The link between the armed policing and crime survey rows is that the information coming out of Police Scotland lacks credibility.

On various occasions recently, officers have told MSPs and the Scottish Police Authority one thing and then had to correct themselves.

For the single force to restore credibility, far greater care must be shown when putting vital statistics into the public domain.