Average weight gain and Average length of stay CAN be used as indicators of programme performance. The question would be whether they are useful to you or not. These calculations can diagnose that you have a problem but will not be useful to indicate what the problem is. Issues of poor compliance by beneficiaries, poor implementation of protocols by staff and poor case finding in the community, among other factors, can dramatically affect both of these performance measures.
A programme with a minimum stay of 8 weeks usually has an average LOS of about 62 days. Average weight gain (AWG) in OTP should be around 5g/kg/day or higher. AWG should be calculated separately for wasted cases and oedema cases.
The minimum stay of 8 weeks is an old discharge criterion which was introduced for MUAC programming many years ago. It was recommended that a child that had not recovered to the discharge criteria after 12 weeks in an outpatient programme despite home visits, should be transferred to inpatient for further assessment. No child should be discharged if they remain below the admission criteria.
The latest WHO recommendation is to use MUAC of 12.5cm as the discharge criterion for MUAC admissions. Weight for height admissions should be discharged by weight for height criteria.
An important point is that the length of recovery depends on the MUAC on admission and the compliance with the treatment regime. Ensuring effective early case finding and good attendance will reduce the length of stay. In a stable context ,the time taken to achieve a MUAC of > 12.5cm can take anywhere between 6 weeks for an 'early' admission and up to 15 weeks for a 'late' admission (e.g. MUAC < 10.5cm). The average LOS for this discharge criterion appears to be around 45 days.
I hope this helps