Hi, I am trying to see if there's a statistical test to compare volumes for an item from two different time periods.
For example, looking at differences between avg. monthly volume for the entire 2018 to 2019 period compared to monthly volume for each month after the start of an intervention (e.g. COVID-19). I have monthly volume for a specific item and it ranges from 2018 to 2020.
I was told that I could do:
However, I'm concerned that:
1. This may not be the right approach (e.g. might require quasi-experimental approach)
2. Degrees of freedom becomes a concern when comparing 1:1 or 1:n
For simple descriptive statistics purposes, is there a way to find whether that change is statistically significant with a p-value with a hypothesis of predicting a decrease in the total volume for each month? Or, would I need to use more advanced econometric techniques to identify if there is a significant difference in volumes for an item between months.
Thank you in advance.
For example, looking at differences between avg. monthly volume for the entire 2018 to 2019 period compared to monthly volume for each month after the start of an intervention (e.g. COVID-19). I have monthly volume for a specific item and it ranges from 2018 to 2020.
I was told that I could do:
Code:
by id, sort : ttest volume, by(post) unequal welch
1. This may not be the right approach (e.g. might require quasi-experimental approach)
2. Degrees of freedom becomes a concern when comparing 1:1 or 1:n
For simple descriptive statistics purposes, is there a way to find whether that change is statistically significant with a p-value with a hypothesis of predicting a decrease in the total volume for each month? Or, would I need to use more advanced econometric techniques to identify if there is a significant difference in volumes for an item between months.
Thank you in advance.
Comment