Is systematic sampling biased

Answer 1

Often not, but it is important to check that there is no systematic pattern in the skip.

To take an unlikely example, suppose you wanted to sample the values of 10% of houses on a street with 200 houses on it. A possible systematic sampling scheme would be to select a random house number to start with and then select every 20th house number (looping back when the number exceeds 200). If the first house number is odd then all houses in the sample are odd numbered and, therefore, on the same side of the street. If the street runs East-West, the sample could consist exclusively of South-facing gardens - attracting a price premium!