# intro(1) - Introduction Populations and Samples Population...

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Introduction Populations and Samples Population - Set of all individuals or units of interest to investigators. Sometimes we may refer to a population of measurements as opposed to individuals or units. Sample - Subset of a population that is observed and measured by investigators.

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Quantitative and Qualitative Variables Quantitaive variables take on numeric values. They can be further classified as: Continuous variables can take on values along an interval (e.g. blood pressure, temperature) Discrete variables can take on distinct values with “breaks” (e.g. Woman’s parity, Number of prior cardiac events) Qualitative variables take on various categories. They can be classified as: Nominal variables take on values with no inherent ordering (e.g. Presence/Absence of parasite, gender, race) Ordinal variables take on categories that can be ordered (e.g. Prognosis, Attitude toward a proposal)
Dependent and Independent Variables Dependent variables are outcomes of interest to investigators. Also referred to as Responses or Endpoints Independent variables are Factors that are often hypothesized to effect the outcomes (levels of dependent variables). Also referred to as Predictor or Explanatory Variables Research ??? Does I.V. D.V.

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Example - Clinical Trials of Cialis Clinical trials conducted worldwide to study efficacy and safety of Cialis (Tadalafil) for ED Patients randomized to Placebo, 10 mg , and 20 mg Co-Primary outcomes: Change from baseline in erectile dysfunction domain if the International Index of Erectile Dysfunction (Numeric) Response to: “Were you able to insert your P… into your partner’s V…?” (Nominal: Yes/No) Response to: “Did your erection last long enough for you to have succesful intercourse?” (Nominal: Yes/No) Source: Carson, et al. (2004).
Example - Clinical Trials of Cialis Population: All adult males suffering from erectile dysfunction Sample: 2102 men with mild-to-severe ED in 11 randomized clinical trials Dependent Variable(s): Co-primary outcomes listed on previous slide Independent Variable: Cialis Dose: (0, 10, 20 mg ) Research Questions: Does use of Cialis improve erectile function?

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Parameters and Statistics Parameters: Numerical descriptive measures for Populations: μ - Mean (average) of a numeric variable σ 2 - Variance - Standard deviation of a numeric variable CV - Coefficient of variation of a numeric variable π - Proportion of population with a nominal characteristic
Parameters and Statistics Statistics: Numerical descriptive measures for Samples Sample Mean (of a sample of size n ): n y y = = ^ μ Sample Variance ( s 2 ) and standard deviation ( s ) : 2 2 2 1 ) ( s s n y y s + = - - = Sample coefficient of variation ( cv ): % 100 = y s cv Sample Proportion with a characteristic: ^ π

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Example - Carbonate of Bismuth Samples of Carbonate of Bismuth from a sample of 6
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## This note was uploaded on 07/28/2011 for the course STA 6934 taught by Professor Young during the Fall '08 term at University of Florida.

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intro(1) - Introduction Populations and Samples Population...

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