1) Provide an example of 4 threats to validity that you have encountered in your research, drawing one from each of the domains Cook and Campbell delineate (statistical conclusion validity, internal validity, construct validity, and external validity).
Statistical conclusion validity: At my institution I found that people would frequently apply various statistical techniques without validating assumptions. For example we wanted to compare gestational age of newborn infants between year epochs. Originally they simply applied a one-way anova. However, they should have first checked for sample size, distributions, and variance to decide which test to use.
Internal validity: I’ve encountered an instrumentation threat in which we were comparing our hematocrit value today compared to those described in the past. However, method of used to calculate hematocrit and should likely be taken into account.
Construct validity: I’ve encountered a construct confounding threat during one of our studies where we wanted to evaluate how long mother’s breast feeding after NICU discharge. Mothers were either discharged with formula fortification or with breast milk with supplemental formula. Initially it appeared as though one was favored over the other but this difference may disappear after we adjust how much mothers were breastfeeding prior to discharge. Still an ongoing investigation so may more to tell =]
External validity: We constantly deal with this threat at our institution which is predominately a low-income community hospital that is a predominately Hispanic population. This often ends up as a limitation for all our studies because it may limit the generalizability especially if it’s a topic with known racial influences.
2) For any data set you frequently use, look up the sample design and describe it.
My team utilizes and prospectively maintained database of all NICU infants. Our studies utilize all infants that meet those particular inclusions so I guess you would call it a convenience sample.