non-random sampling random sampling sampling population quantitative qualitative geographical chronological types of classification unpublished data published data schedules sent-investigators questionnaires sent-mail information from correspondents indirect oral interviews direct personal interview spacio-temporal data spatial data time series data secondary data primary data demerits of tabulation merits of tabulation manifold table two way table one way table parts of table complex tabulation simple tabulation cartogram pictogram piediagram bar diagram line diagram ungrouped data grouped data percentiles mode median arithmetic mean central tendancy okazaki fragments dispersive semiconservative conservative replication dna
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