What is the difference between pooled cross sectional data and panel data? They seem so similar. Are they the same thing but just referred to as different names?
 A: Cross-sectional data, or a cross section of a study population, in statistics and econometrics is a type of one- dimensional data set. Cross-sectional data refers to data collected by
observing many subjects (such as
individuals, firms or countries/regions)
at the same point of time, or without
regard to differences in time. Analysis
of cross-sectional data usually consists of comparing the differences among the
subjects. For example, we want to measure
current obesity levels in a population.
We could draw a sample of 1,000
people randomly from that population
(also known as a cross section of that
population), measure their weight and height, and calculate what percentage
of that sample is categorized as obese.
For example, 30% of our sample were
categorized as obese. This cross-
sectional sample provides us with a
snapshot of that population, at that one point in time. Note that we do not
know based on one cross-sectional
sample if obesity is increasing or
decreasing; we can only describe the
current proportion. Cross-sectional data differs from time series data also known as longitudinal data, which follows one subject's changes over the course of time.
Another variant, panel data (or time- series cross-sectional (TSCS) data),
combines both and looks at multiple
subjects and how they change over the
course of time. Panel analysis uses panel data to examine changes in
variables over time and differences in
variables between subjects. In a rolling cross-section, both the
presence of an individual in the sample
and the time at which the individual is
included in the sample are determined
randomly. For example, a political poll
may decide to interview 100,000 individuals. It first selects these
individuals randomly from the entire
population. It then assigns a random
date to each individual. This is the
random date on which that individual
will be interviewed, and thus included in the survey.
A: When I see panel data, I think longitudinal data, so observations collected on the same individuals at multiple times, on the same topics. Repeated cross sections should be the same topics, but you get different samples of individuals at each observation.  I'd welcome other descriptions.
A: The answer here is pretty straight forward:
Both pooled cross sectional data and pure panel data collect data over time (this can range from 2 time periods to any large number). The key difference between the two is the "units" we follow. I am defining units as households, countries, or whatever we are collecting data on. 
In pooled cross section, we will take random samples in different time periods, of different units, i.e. each sample we take, will be populated by different individuals. This is often used to see the impact of policy or programmes. For example we will take household income data on households X, Y and Z, in 1990. And then we will take the same income data on households G, F and A in 1995. Although we are interested in the same data, we are taking different samples (using different households) in different time periods. 
In pure panel data, we are following the same units i.e. the same households or individuals over time. For example we will follow the same set of households X, Y and Z, for each time period we collect data i.e. in 1990 and we will also interview the same households in 1995.
Therefore the fundamental difference, is simply the units we observe the data for.
Hope this helps.
A: Based on the definition of Corey, we have following methodology to estimate the model with the pooled cross-sectional data and panel data. 
Pooled cross section: one way fixed effects or random effects (only time) or just pooled OLS. 
Panel data: two (or one) way fixed effects/random effects (either time or individual or both) or pooled OLS. 
A: This is from "Basic Econometrics" by Gujarati (4th Edition, P28):
Panel, Longitudinal, or Micropanel Data This is a special type of
pooled data in which the same cross-sectional unit (say, a family or a firm)
is surveyed over time. For example, the U.S. Department of Commerce carries
out a census of housing at periodic intervals. At each periodic survey the
same household (or the people living at the same address) is interviewed to
find out if there has been any change in the housing and financial conditions
of that household since the last survey. By interviewing the same household
periodically, the panel data provides very useful information on the dynamics
of household behavior.
A: Pooled data is also panel data but the inverse is not true.
