Data

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data observations that have been collected statistics collection of methods for planning studies and experiments, obtaining data, and then organizing, summarizing, presenting, analyzing, interpreting, and drawing conclustions based on the data. population complete collection of all elements to be studied. Complete because it includes all subjects to be studied. census collection of data from EVERY member of population sample SUBCOLLECTION of members selected from a population parameter numerical measurement describing some characteristic of a POPULATION statistic numerical measurement describing some characteristic of a SAMPLE quantitative data consist of numbers representing counts or measurements qualitative data can be separated into different categories that are distinguished by some nonnumeric characteristic discrete data result when # of possible values is either a finite number or a "countable" number continuous data result from infinitely many possible values that correspond to some continuous scale that covers a range of values without gaps, interruptions or jumps. nominal level of measurement characterized by data that consist of names, labels, or categories only. Cannot be arranged in an ordering scheme. ordinal level of measurement can be arranged in some order, but differences between data values either cannot be determined or are meaningless. interval level of measurement like ordinal, but difference between any 2 data values is meaningful. ratio level of measurement interval level with additional property that there is also a natural zero starting point. voluntary response sample respondents themselves decide whether to be included observational study observe and measure specific characteristics but don't MODIFY subjects experiment apply some TREATMENT and then proceed to observe its effects on the subjects (experimental units) cross-sectional study data are observed, measured, and collected retrospective study data collected from the past by going back in time prospective study data collected in the future from groups sharing common factors confounding not able to distinguish among effects of different factors placebo effect when an untreated subject incorrectly believes that he/she is receiving a real treatment and reports an improvement in symptoms blinding subject doesn't know whether he/she is receiving a treatment or a placebo. double-blind blinding occured at 2 levels random sample members from population are selected in such a way that each INDIVIDUAL MEMBER has and equal chance of being selected simple random sample n subjects are selected so that every possible sample of the same size n has the same chance of being chosen probability sample selecting members from a population in a way that each member has a known chance of being selected. systematic sampling select a starting point then select every kth (10th, 50th, etc) element in the population convenience sampling use results that are easy to get stratified sampling subdivide the population into at least 2 different subgroups so that subjects within same subgroup share same characteristics cluster sampling divide population into sections then randomly select some of those clusters and then choose ALL members from selected clusters