the question is: by utilizing DiD (difference in difference) get a consistent estimate of the given example. define conditions of reliable control in next part. for details please the below:

2. School closures have been among the most common non-pharmaceutical interventions to slow down the spread of the novel coronavirus. Despite the large, expected costs of school closures for human capital formation, little is known about their impact. A recent paper titled "School re-openings after summer breaks in Germany did not increase SARS-CoV-2 Cases" analyses how the opening of schools affects COVID cases, exploiting the timing of school re-openings across German states after the summer of 2020.1 In Germany, start and end dates of summer breaks differ between states to prevent the entire German population from going on holiday at the same time. The staggered summer breaks avoid traffic congestion as well as excess demand for holiday accommodation in tourist regions. The school year 2019/2020 ended as planned between 22 June and 30 July followed by summer breaks of six weeks. After the summer, schools were re-opened across all Germany, following this staggered timing. The authors focus on this phase of full re-opening of schools in all states after the summer breaks which took place from early-August to mid-September 2020. Figure 2 displays the spatial and temporal variation in school starting dates after the summer break across German states and Figure 4 plots the point estimates and the 95% confidence intervals from a standard event study model comparing the evolution of the treatment and control groups.3 Auguil 6 August 10 August 12 August 17 August 27 August 31 August Figure 2: School Opening Dates after Summer Vacation 2020 in Germany Note: This graph shows a map of German counties highlighting the counties in states by date of school opening after summer vacation 2020. Counties (states) highlighted in dark grey start the new school year on the respective date, while light grey indicates that they are still on summer vacation and medium grey indicates that they had already re-opened schools at an earlier date. Schools re-openings: 3 August: Mecklenburg-Vorpommern, 6 August: Hamburg, 10 August: Schleswig-Holstein, Berlin, Brandenburg, 17 August: Hessia, Rhineland-Palatinate, and Saarland, 27 August: Lower Saxony, Bremen, and Saxony-Anhalt, 31 August: Saxony and Thuringa, 8 September: Bavaria, 14 September: Baden-Wuerttemberg. Source: KMK.All ages 5. B22 = -0.55 -5 M -1.51 -15 -10 -5 0 5 10 15 20 Days relative to end of summer break Point estimates 95% CI Figure 4: The Effect of the End of Summer Breaks on Confirmed Cases Note: This graph plots the point estimates (Or,T E [-15, 22)) and corresponding 95% percent confidence intervals of the event study model as defined in Equation (). The dependent variable is the daily count of confirmed cases per 100K population per county. The vertical line at 7 = 0 indicates the school opening. The regressions include fixed effects on the county and day level. Standard errors are clustered at the federal state level.