population and sample variable

[Nandni Gupta]

when are we supposed to use the population variance covariance and when the sample ones. If it is just not mentioned than which should we choose as in lectures somewhere we use population ones and somewhere sample ones. Is sample mean and population mean same since in the week 4 practice assignment solution N was used in sample mean in place of N-1.

[Nikita Kumari]

Hello Nandni,

In case of sample mean, you should not divide the sum by (n-1) observations. Both for calculating the sample mean and the population mean, you should divide  the sum by n. 

In case it is explicitly mentioned in the question to find the sample variance or covariance, then use the formula for sample, otherwise use the population formula.

Thanks

Nikita

Statistics course support team

[Sanchi Priyanshu]

so nikita  please clarify ,

everytime in any formula of variance,s.d,corelation, covariance

 we have to use mean as denominator with n only  and main formula according to sample or population given in question

and  my second doubt is

if in question it is written to find  ,s.d,corelation, covariance,variance ,we have to find sample or population or will it be written evrtytime in question which of the 2 we have to use

cause every formula has n occurring in it

cause inn week4 of stats 2nd  question of MSQ of practice assignment, the corelation of father and daughter,n used was 8 so shouldnt it be used 7 as it is not written in question so why didnt we write 7