La Rosa, Gabrielle Anne D. Med- 2AJuly 27, 2015

1. Differentiate Validity and Precision in epidemiologic studies

In epidemiologic observations, the quality of data is often described based on validity and precision. These two terms are components of accuracy. Validity is the extent to which the study measures what it is intended to measure. It is concerned with the accuracy of the test procedure. Lack of validity is referred to as "bias" or "systematic error."

Precision is the reproducibility of a study result, that is, the degree of resemblance among study results. Lack of precision is referred to as "random error". A study that is based on information from too few subjects allows for considerable random variation in the study result since only a few extra cases occurring in one or another category would substantially affect the results. Such a study would have a low precision.

The validity and precision of studies are parts of a good practice in measurement in both research, epidemiology, and clinical settings. It is important to know these concepts so that data and results gathered will not be compromised by inadequate and inappropriate measurement processes and tools.2. Compare External validity and Internal validityInternal validity refers to the validity of the inferences drawn as they pertain to the members of the source population. It is concerned with the design characteristics of experimental studies. External validity concerns inferences about an external population beyond the study's restricted interest. It is concerned with the researchers ability to generalize his or her findings to other samples and settings. It is affected by the sample size, the method of sampling, and the design characteristics and measures used in the study. It is the validity of inferences as they pertain to people outside that population.3. Discuss the ways to assess the reliability of epidemiology measurements

Reliability is the property of reproducibility of the results of a measurement, procedure or tool. There are several different ways in which reliability can be assessed. These include test-retest reliability, inter-observer reliability, and internal consistency.

In test- retest reliability (intra-observer reliability), the same test is administered twice to the same participants. The results obtained from the first test are then correlated with the second test. Reliability is generally measure by a correlation coefficient that may vary from -1 to +1 in value.

In inter-observer (inter-rater reliability, the extent of agreement is generally determined by having two or more clinicians independently assess the same patients and then comparing the results using correlations. If the agreement (correlation) is high then we have high inter-observer or inter-rater reliability.

The internal consistency of the test is the extent to which the results on the different items correlate with each other. It is also measured by a form of correlation coefficient known as Cronbach alpha. These ways of assessing reliability are important in epidemiological studies because a high degree of reliability is necessary for minimizing measurement error.