That arises from inaccurate sampling frame, data clarification or verification methods, reporting or coding of data, and/or specifications. It may also arise from poorly designed survey questionnaires, improper sample allocation and selection procedures, and/or errors in estimation methodology.
riff (rÉªf) n. 1. an ostinato melodic phrase accompanying a soloist in jazz or rock music. 2. any variation or improvisation, as on an idea. v.i. 3. to perform a riff. [1930â35; perhaps alter. of refrain 2] riff Past participle: riffed Gerund: riffing
Writer: Mick Jagger, Keith Richards. Producer: Andrew Loog Oldham. Released: May '65, London. 14 weeks; No. 1. It's the riff heard  round the world, says Steve Van Zandt, guitarist for the E Street Band. The riff came to Keith Richards in a dream one night in May 1965, in his motel room in Clearwater, Florida, on the Rolling Stones' third U.S. tour. He woke up and grabbed a guitar and a cassette machine.